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CVE-2026-99007
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/fb-helper: defer setup when fbdev_probe() fails, not just on -EAGAIN
__drm_fb_helper_initial_config_and_unlock() calls
drm_client_modeset_probe() first, which already fills in each
mode_set-mode/num_connectors for every connected output, and only
afterwards calls drm_fb_helper_single_fb_probe() to create
fb_helper->fb and wire it into those mode_sets via
drm_setup_crtcs_fb().
If drm_fb_helper_single_fb_probe() fails with anything other than
-EAGAIN (e.g. dev->driver->fbdev_probe() itself fails), the function
bails out before drm_setup_crtcs_fb() runs and before setting
fb_helper->deferred_setup. The client is left with mode_sets that
have a mode and connectors but mode_set->fb == NULL, and nothing
marks this fb_helper as needing a retry.
__drm_fb_helper_restore_fbdev_mode_unlocked() only skips committing
when fb_helper->deferred_setup is set, so a later .restore() call
(drm_lastclose() on process exit, in this report) commits the stale
mode_set through drm_client_modeset_commit() ->
drm_client_modeset_commit_atomic() -> __drm_atomic_helper_set_config(),
which hits WARN_ON(!set->fb).
Mark fb_helper->deferred_setup on any drm_fb_helper_single_fb_probe()
failure, not just -EAGAIN, so restore keeps skipping the commit until
a later hotplug event successfully re-probes and re-populates
mode_set->fb. The real error code is still returned to the caller
unchanged.
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CVE-2026-99006
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/i915/gem: Prevent overstepping exec array boundary
It is possible for eb_relocate_parse_slow() to call kvfree() on
entries outside the original exec array during following
scenario inside eb_relocate_parse_slow():
1) eb_copy_relocations() allocates as many as eb-buffer_count
copies for exec entries;
2) eb_parse() appends up to two VMAs, right after incrementing
eb->buffer_count;
3) cleanup under "out" label uses this incremented buffer_count
to release relocation pointers from exec array via kvfree(),
not from VMA array.
To amend this problem, ensure that relocation cleanup uses the
original exec object count, excluding the VMAs appended by the
command parser.
(cherry picked from commit 2a0158925fb943c7ba8f3216e2734952128defc9)
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CVE-2026-99005
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/i915/gt: Unmask interrupts only when ACTIVE is true
There is a small race window between intel_rps_boost() reading
a stale ACTIVE state and queuing rps-work, where ACTIVE may be
changed via asynchronous calls triggered by wakeref drop.
This means that rps_work() could be triggered after the GT has
been parked, so unmasking RPS PM interrupts would happen without
holding PM wakelock. This sequence of events may be observed
during live_rc6_ctx_wa() selftest:
1) live_rc6_ctx_wa()
-> intel_engine_pm_put()
-> wakeref_put()
ASYNC1) wakeref_put() callback
-> __engine_park()
-> intel_gt_pm_put_async()
-> intel_gt_pm_put_async_untracked()
-> intel_wakeref_put_async()
ASYNC2) wakeref_put_async() callback
-> __gt_park()
-> intel_rps_park()
-> intel_rps_clear_active() [clear ACTIVE]
WITH INTERRUPTS:
-> rps_disable_interrupts()
-> cancel_work_sync(rps->work)
-> rps_reset_interrupts() [rps->pm_iir = 0]
WITHOUT INTERRUPTS (TIMER mode):
-> rps_stop_timer()
-> cancel_work_sync(rps->work)
2) live_rc6_ctx_wa()
-> intel_gt_wait_for_idle()
-> intel_gt_retire_requests_timeout()
-> dma_fence_wait_timeout()
-> ops->wait() [i915_fence_wait()]
-> i915_request_wait_timeout()
-> intel_rps_boost()
-> intel_rps_is_active() [check ACTIVE]
[OPEN RACE WINDOW]
-> queue_work(rps->work)
-> retire_requests()
-> i915_request_retire()
-> intel_rps_dec_waiters() [from 1 to 0]
If ASYNC1 and ASYNC2 would execute during [OPEN RACE WINDOW],
then:
3) rps_work() executes from the workqueue and may satisfy
"(!pm_iir && !client_boost)" test (in TIMER mode rps->pm_iir
is zeroed by an earlier rps_work() call or never gets a new
value after previous intel_rps_unpark() event), so it jumps
to "out" label, bypassing intel_rps_is_active() guard and
executes gen6_gt_pm_unmask_irq();
4) GT is parked and runtime PM wakelock is dropped, so only
a raw reference in __gt_park() ->
intel_display_power_put_async() remains for 100ms, then the
MMIO write in gen6_gt_pm_unmask_irq() detects missing
wakelock via assert_rpm_wakelock_held() and emits
"RPM wakelock ref not held during HW access" tainting kernel.
Commit 3e7abf814193 ("drm/i915: Extract GT render power state management")
dropped the "if (rps->interrupts_enabled)" guard that
gen6_pm_rps_work() had around this unmask in i915_irq.c.
INTEL_RPS_ACTIVE brackets the same window, since it is set in
intel_rps_unpark() before rps_enable_interrupts() and
rps_start_timer() and cleared in intel_rps_park() before
rps_stop_timer() and rps_disable_interrupts().
Skip unmasking when RPS is no longer active (reaching unmask
operation is independent of INTERRUPT mode). This does not
prevent RPS operation from resuming on the next unpark.
In interrupt mode, intel_rps_unpark() calls
rps_enable_interrupts(), which enables and unmasks the PM
interrupts. In timer mode, it calls rps_start_timer(),
restarting periodic engine-busyness evaluation. The timer
generates software RPS events and queues rps_work() directly,
independently of PM interrupt delivery. Neither mode requires
the late worker to unmask interrupts while the GT is parked
(cherry picked from commit ca4a6deadad15b91ee083afe445fa6bdbfb68206)
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CVE-2026-99004
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/imagination: Size page table preallocation by device address
Commit 0a8224058a58 ("drm/imagination: Fix page count for page table for
map() interface") passed the device address to
pvr_mmu_op_context_create(), but the preallocation is still sized from
device_addr + sgt_offset with an exclusive end. The offset into the
object's pages has no place in a device-virtual range, and the exclusive
end allocates one table too many when the range ends on a table
boundary.
Count the tables from device_addr and the inclusive end of the range.
The new calculation does not take page table indices into account. This
fixes another issue with the previous implementation, where the
difference between start and end indices could underflow when a mapping
crossed a page table boundary. This would lead to the driver
preallocating a huge number of MMU pages, exhausting system memory and
triggering an out of memory panic.
[Alessio: add paragraph to point out OOM bug being fixed, cc stable]
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CVE-2026-99003
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/panthor: validate userspace queue count against initialized firmware slot count
In panthor_drv.c:panthor_ioctl_group_create(),
the queue count is validated against the hardcoded maximum:
if (!args-queues.count || args->queues.count > MAX_CS_PER_CSG)
return -EINVAL;
However, if the firmware reports fewer slots than MAX_CS_PER_CSG,
panthor_fw_init_ifaces() will only initialize that smaller number of
stream interfaces.
If unprivileged userspace requests more queues than the firmware reported
(but no more than MAX_CS_PER_CSG), cs_slot_prog_locked() fetches an
uninitialized stream interface and may crash when dereferencing
cs_iface->input->ringbuf_base.
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CVE-2026-99002
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/vmwgfx: validate pitch coming from userspace
Validate the pitch, alongside the box dimensions before trying
to copy data from the underlying surface. Fixes possible
out of bounds reads with cursor snooping.
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CVE-2026-99001
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/xe/i2c: cancel the client work on remove
xe_i2c_notifier() stores the DesignWare adapter in i2c-adapter and
schedules i2c->work when the adapter is registered under the xe I2C
platform device, and xe_i2c_client_work() then instantiates the AMC
client device on that adapter.
xe_i2c_remove() tears down the AMC, unregisters the client devices,
the bus notifier and the adapter platform device, but it never drains
i2c->work. A work item that is still queued or running when the
adapter is unregistered dereferences i2c->adapter in
i2c_new_client_device() after platform_device_unregister() has
released the adapter. The work item is also embedded in the
devm-allocated struct xe_i2c, so a work item still queued after the
drm device devm unwind frees that allocation runs its callback on
freed memory.
The bus notifier is the only thing that schedules this work, and it is
unregistered after the client devices. An instance that is still queued
when the teardown runs can therefore write
i2c->client[XE_I2C_CLIENT_AMC] while the loop is unregistering and
clearing the same array, and an AMC client it instantiates late is only
cleaned up by the adapter's own child sweep in i2c_del_adapter().
Move bus_unregister_notifier() in front of the client teardown loop
and cancel the work right after it, so no new instance can be
scheduled and a queued instance is drained before the client array is
touched. A running instance still finds a live adapter, since the
adapter is unregistered later.
(cherry picked from commit a23f27d5ec11c3f418c5e5531eea34ccda2b5b20)
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CVE-2026-99000
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/xe: Fix shrinker accounting double-subtraction on nested external pins
xe_bo_pin_external() and xe_bo_unpin_external() support nested pins,
since the underlying ttm_bo_pin()/ttm_bo_unpin() maintain a pin_count
refcount rather than a boolean. However, the shrinker accounting calls
xe_ttm_tt_account_subtract() and xe_ttm_tt_account_add() are invoked
unconditionally on every pin_external()/unpin_external() call, instead
of only on the transition into and out of the pinned state.
An external BO (dma-buf) can be pinned more than once while already
pinned, for example when it has multiple attachments/importers, each
independently calling xe_bo_pin_external(). Each such nested pin
subtracts the BO's pages from the shrinker's accounting again, even
though the BO's pages were already removed from consideration by the
first pin. Symmetrically, each nested unpin adds them back again
before the BO is actually unpinned. This desynchronizes the
shrinker's page and object counts from reality, and since they are
declared as signed long but interpreted as unsigned long in
xe_shrinker_count(), the underflow can turn into an enormous
shrinkable/purgeable page count, causing the shrinker to be invoked
excessively under memory pressure.
Guard the accounting calls with the same pin-count transition checks
already used to guard the pinned_link list maintenance, so accounting
is only updated on the outermost pin and the final unpin.
While centralizing this logic into xe_bo_account_pin()/
xe_bo_account_unpin(), also close a second, related accounting gap
affecting imported dma-bufs. For an imported bo's ttm_tt, xe's
ttm_tt_populate hook (xe_ttm_tt_populate()) early-returns without
calling xe_ttm_tt_account_add(), since TTM_TT_FLAG_EXTERNAL is set
without TTM_TT_FLAG_EXTERNAL_MAPPABLE. However, TTM core's
ttm_tt_populate() wrapper unconditionally marks the tt as populated
on driver-hook success, so ttm_tt_is_populated() still reports true
for it. xe_bo_account_pin()/xe_bo_account_unpin() trusted
ttm_tt_is_populated() as a proxy for "these pages are accounted for
by the shrinker", and would subtract/add pages for such a tt that
were never added in the first place, again underflowing the
shrinker's counts. This is reachable today via xe_bo_pin_external(),
and would have become newly reachable via the fb-pin path once this
patch routes __xe_pin_fb_vma() through xe_bo_pin_account() below, so
fix it here rather than in a later patch, to avoid a commit in this
series that introduces the regression before fixing it. Skip the
accounting for imported bos, using the same EXTERNAL &&
!EXTERNAL_MAPPABLE test xe_ttm_tt_populate()/xe_ttm_tt_unpopulate()
use to decide whether to act, via a new xe_ttm_bo_is_imported()
helper (hoisted up from its only prior use site).
v2:
- Fix the critical issue caught by Sashiko AI review: the pin-count
transition check introduced here was still bypassed by the fb-pin
path (__xe_pin_fb_vma()/__xe_unpin_fb_vma()), which could leave a
stale pinned_link entry and a permanent shrinker accounting leak
when the fb-unpin performed the true last unpin. Addressed in a
separate follow-up patch in this series rather than folded in here,
since it is a distinct bug with its own Fixes: tag.
- Drop the unneeded local "last_unpin" variable in
xe_bo_unpin_external(), restoring the original inline
bo-ttm.pin_count == 1 check; it was a no-op rename not used by any
of the new accounting helpers, and was going to be deleted again by
the follow-up patch anyway.
v3:
- Exclude imported dma-bufs from the pin/unpin shrinker accounting,
fixing another underflow caught by Sashiko AI review.
- Add a short comment on the backup-object pin site noting it's
already populated/accounted at pin time, addressing (as a
false-positive clarification, no code fix needed) a separate
Medium-severity accounting-leak concern also caught by Sashiko AI
---truncated---
-
CVE-2026-98999
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/xe: Fix stale pinned_link entry when fb-pin performs the final unpin
xe_bo_pin_external() and xe_bo_unpin_external() maintain the bo's
pinned_link list membership in xe-pinned.late.external, based on
whether the current call is the outermost pin or the final unpin.
However, the same external bo's pin_count can also be raised and
lowered directly by __xe_pin_fb_vma()/__xe_unpin_fb_vma(), which pin
the bo as a display scanout buffer without going through
xe_bo_pin_external()/xe_bo_unpin_external() at all, and have no
notion of, or ownership over, pinned_link.
If a bo is pinned both externally (e.g. dma-buf export) and as an fb,
and the external unpin happens first, xe_bo_unpin_external() correctly
observes pin_count > 1 and leaves the bo on pinned_link. When the fb
unpin later performs the true last unpin (pin_count 1 -> 0), it never
touches pinned_link, leaving the bo linked on xe->pinned.late.external
indefinitely. Once the bo is subsequently freed, this stale list entry
points into freed memory, corrupting the list and risking a
use-after-free the next time the list is walked or spliced.
The backup object pin/unpin sites in xe_bo_notifier_prepare_pinned()/
xe_bo_notifier_unprepare_pinned() have the same bypass characteristic,
though they never add their bo to a pinned list, so are not affected
by this particular list-corruption issue.
Move the pinned_link removal into xe_bo_account_unpin(), which already
runs on every unpin path (kernel, external, framebuffer, backup
object) right before the true 1 -> 0 pin_count transition. Since
list_del_init() only operates on the node itself, this removal is
list-agnostic and safe to perform regardless of which list (external
or kernel_bo_present) the bo happens to be linked on, or which code
path is performing the final unpin. Drop the now-redundant explicit
list_del_init() calls in xe_bo_unpin_external() and xe_bo_unpin().
v2:
- New patch
v3:
- Rebased on changes to previous patch.
(cherry picked from commit ca58d36a1f93af586ee93b340c9f9fd81312cc01)
-
CVE-2026-98998
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/bridge: th1520-dw-hdmi: Fix remove() callback
This driver stores struct th1520_hdmi * in platform drvdata, but
th1520_dw_hdmi_remove() was reading it back as struct dw_hdmi *
and passing it to dw_hdmi_remove(), so teardown runs on the wrong
pointer.
Retrieve struct th1520_hdmi * from platform drvdata and pass
hdmi-dw_hdmi to dw_hdmi_remove().
-
CVE-2026-98997
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu/userq: only accept doorbell BOs as queue doorbell
amdgpu_userq_get_doorbell_index() pins any BO passed as doorbell_handle
into the doorbell domain. For a regular BO, TTM moves it with
ttm_bo_move_null() and its contents are lost. Since an importer on the
same device gets the exporter's GEM object, a client can do this to a
buffer another client shared with it.
Reject BOs that were not created in the doorbell domain.
v2: drop the error message, use a local abo variable (Christian)
(cherry picked from commit f7497bbc19db4821c62b9d97b31c9086feb2d917)
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CVE-2026-98996
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
fs: don't silently unmount busy mounts
The propagate_mount_busy() helper exists to decide whether a synchronous
can suceed. It does that by looking at the copies of the victims in the
mounts its parent propagates to. One of those functions from propagation
hell.
It skips a copy that has child mounts except for the case of a single
child mount covering the copy's root. That algorithm used to be exact.
It isn't anymore.
Originally only childless copies were unmounted during propagation.
And 1064f874abc0 ("mnt: Tuck mounts under others instead of creating
shadow/side mounts.") ended up adding covered mounts to both sides in
one go.
Along came 99b19d16471e ("mnt: In propgate_umount handle visiting mounts
in any order") and that started to unmount more than before:
[1]: A copy of a mount is unmounted when each of its children is either
its overmount or a copy of the victim itself. In the former case
the overmount gets reparented. In the latter case the copy of the
victim will end up being unmounted.
So propagate_umount() ended up being rewritten without adjusting
propagate_mount_busy(). And currently propagate_mount_busy() doesn't
look at copies of the victim that have two or more children nor a single
child that is not the overmount.
So any such copy in [1] is not checked for
references. The result is that a synchronous unmount succeeds, pulling
out a mount that is still in use.
A container can run into this with its own mounts. The host shares a
tree with the container and the host has a mount in that tree:
mount -t tmpfs none /mnt
mount --make-shared /mnt
mount -t tmpfs none /mnt/a
The container's /mnt is a slave copy of the host mount. The container
now takes a detached copy of the tree and mounts that copy beneath its
propagated copy of /mnt/a and keeps the file descriptor to the tree
open:
unshare -m --propagation unchanged
mount --make-rslave /
fd = open_tree(AT_FDCWD, "/mnt", OPEN_TREE_CLONE | AT_RECURSIVE)
move_mount(fd, "", AT_FDCWD, "/mnt/a", MOVE_MOUNT_BENEATH)
grep /mnt /proc/self/mountinfo
775 355 ... /mnt ... master:646
777 775 ... /mnt/a ... master:646
776 777 ... /mnt/a ... master:647
778 777 ... /mnt/a/a ... master:647
The now attached tree (777) is now mounted beneath the container's copy
of /mnt/a. That's also where the host mount sits (as seen from the host
mount namespace). So the propagated copy (776) of the host's mount is on
top of its root and the copy of that (778) is inside it. Now the host
runs:
umount /mnt/a
and it succeeds. The moved tree tree and the copy inside of it are gone
from the container. Now only the propagated copy is left and it got
reparented to where it was before:
grep /mnt /proc/self/mountinfo
775 355 ... /mnt ... master:646
776 775 ... /mnt/a ...
But the file descriptor still refers to the moved tree. So a synchronous
umount detached a mount that is still in use.
Teach propagate_mount_busy() the same checks that propagate_umount()
does. It now checks for a single victim mount without children
for which it can assume that MNT_LOCKED is cleared on every copy like
propagate_umount() does. The copies form chains. IOW, when a copy itself
receives propagation from the victim's parent then the mount at the same
mountpoint inside that copy is a copy as well. Whether a mount receives
propagation from the victim's can simply be checked by walking its
masters. Walk each chain once from its top so we are sure that nested
copies stay linear. Check every reference once of every copy that gets
unmounted.
-
CVE-2026-98995
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: reset the old parent's -overmount in mnt_change_mountpoint()
__umount_mnt() resets ->overmount of the parent when it unmounts the
mount that overmounts it. mnt_change_mountpoint() doesn't. It moves the
mount to its new parent and leaves the old one pointing at it.
For a mount that is moved beneath in attach_recursive_mnt() that doesn't
matter. The new mount has already reset ->overmount of the old parent by
the time the old top mount is moved onto it.
It matters for reparent() though. propagate_umount() moves a surviving
overmount onto the first ancestor that isn't going to be unmounted. The
mount it was taken from is unmounted immediately afterwards. If a file
descriptor keeps that unmounted mount alive ->overmount points at the
moved mount. That's a dangling pointer and UAF as the moved mount is
unmounted and freed.
do_lock_mount() follows ->overmount from the target path under
mount_lock. With a file descriptor on such a mount as the target of a
mount beneath topmost_overmount() walks into the freed mount and
do_lock_mount() takes references on whatever it finds there.
So reset ->overmount of the old parent in mnt_change_mountpoint() the
same way __umount_mnt() does. A mount's ->overmount is then always a
mount that is attached to it.
-
CVE-2026-98994
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
statmount: read the parent of an unmounted mount under mount_lock
statmount_mnt_basic() reads the ids of the parent through m-mnt_parent
with namespace_sem held for reading. That's fine for a mount that is
in a namespace. Everything above it is pinned by that namespace.
STATMOUNT_BY_FD also accepts a file descriptor on a mount that has
been unmounted on purpose and that only the file descriptor keeps alive.
If that mount stayed attached to its parent when it was unmounted the
parent is unmounted as well and nothing pins it for the child.
The final mntput() unmounts the children under mount_lock alone and
frees the parent afterwards. Concurrently, statmount_mnt_basic() reads
m->mnt_parent twice while that can happen and can easily dereference a
mount that's already gone.
Read the parent of an unmounted mount under mount_lock. The parent
can't be put while it is held and both ids come from the same mount. A
mounted mount's parent is pinned by the namespace and a mount can't
leave its namespace while namespace_sem is held, so the common case
takes no global lock.
-
CVE-2026-98993
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: don't inherit MNT_UMOUNT in clone_mnt()
MNT_UMOUNT gets raised on a mount that umount_tree() or umount_one() has
taken out of its namespace. It's never cleared. __detach_mounts()
unhooks a mount that carries it instead of unmounting it.
disconnect_mount() lets an unmounted child stay attached only if its
parent carries it. propagate_umount() takes it as the sign that a mount
is going to be unmounted when it decides what else can be unmounted,
where a chain of locked mounts ends and where a for reparenting an
overmount.
clone_mnt() copies the flags of the source and only masks
MNT_INTERNAL_FLAGS which doesn't include MNT_UMOUNT. A mount that was
lazily unmounted but is kept alive by a file descriptor can still be
copied when its root is an nsfs or pidfs file because may_copy_tree()
accepts those before checking whether the source is mounted at all:
mount --bind /proc/self/ns/net /tmp/x
exec 3 /tmp/x
umount -l /tmp/x
mount --bind /proc/self/fd/3 /tmp/y
The mount on /tmp/y is attached to the caller's namespace with
MNT_UMOUNT already set and every copy of it inherits the flag again.
That causes a number of bugs:
- Unlink its mountpoint from a mount namespace where it isn't one.
__detach_mounts() takes it for a mount that was unmounted earlier,
unhooks it from its parent and drops the reference the namespace
holds on it. It stays in the namespace with one reference too few
and as its own parent, so it can't be unmounted through the file
descriptor anymore and the namespace never finds it again. When the
namespace goes away it's leaked and points to a freed struct
mnt_namespace that may_change_propagation() and anon_ns_root() read
on the next propagation change or mount_setattr() through the file
descriptor.
- Make it shared and unmount a peer. trace_transfers() follows the
flag from the peer into it and strips it from its peer group.
- Let a propagated umount reach it. gather_candidates() marks it with
T_UMOUNT_CANDIDATE but never puts it on the candidate list, so the
mark is never cleared and every later propagated umount skips it. If
it's the parent of a locked mount handle_locked() takes it as the
cutoff and commits the locked child that should have stayed and
disconnect_mount() leaves that child attached to it, unmounted under
a mounted parent, which is what disconnect_mount() exists to
prevent. When the namespace goes away umount_tree() visits the child
a second time. And once __detach_mounts() has made it its own parent
reparent() never finds the end of the chain of unmounted parents.
A clone is a new mount that has never been unmounted. Add MNT_UMOUNT
to MNT_INTERNAL_FLAGS so clone_mnt() never copies it. And warn when
umount_tree() reaches a mount that already has it set.
-
CVE-2026-98992
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: don't copy an unmounted mount tree
may_copy_tree() accepts a mount whose root is an nsfs or pidfs file
before it checks whether that mount is mounted. This exception exists
for nsfs and pidfs mounts. They are part of no mount namespace so
neither check_mnt() nor is_mounted() would let them through and
bind-mounting a nsfsfd or a pidfd wouldn't work.
Problem is that exception also admits a bind mount of such a file when
it was lazily unmounted and is only kept alive by a file descriptor:
mount --bind /proc/self/ns/net /tmp/x
exec 3 /tmp/x
umount -l /tmp/x
mount --rbind /proc/self/fd/3 /tmp/y
With MS_REC or AT_RECURSIVE copy_tree() doesn't stop at the unmounted
mount. It copies every mount that stayed attached to it as well. So if
you have a bunch of overmounts over the nsfsfd or the pidfd the whole
unmounted stack is copied. That's a bug.
So refuse to walk an unmounted tree. Copying its root alone stays
possible. So a bind mount of a namespace that is gone can still be
recreated from a file descriptor on the old one. The file descriptor
pins that mount and its root and __has_locked_children() only reads the
direct children which don't leave the parent's list without
namespace_sem. The internal mounts carry MNT_NS_INTERNAL instead of NULL
and are still walked. Copying an unmounted tree recursively fails with
EINVAL.
-
CVE-2026-98991
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: queue a mount only once for mount notifications
mnt_notify_add() puts a mount on notify_list. It doesn't check whether
the mount is on the list already. That's fine as long as every mount is
queued at most once per namespace_sem hold. It isn't.
propagate_umount() moves a surviving overmount off a stack of mounts
that are going away and queues it as moved. shrink_submounts() and
mark_mounts_for_expiry() call umount_tree() for several mounts under a
single namespace_sem hold. So the second umount_tree() can take down
exactly the mount the first one reparented, reparent it once more and so
end up queueing it a second time.
The second list_add_tail() cuts the mounts queued in between out of the
list while the head still points at the last of them. notify_mnt_list()
then only visits that one mount and the others are freed after the grace
period with notify_list still pointing at them. Every later mount
operation on the host walks freed memory:
BUG: KASAN: slab-use-after-free in __list_add_valid_or_report
Read of size 8 at addr ffff8881003d57e0 by task notify_dq/162
__list_add_valid_or_report+0x15c/0x1a0
mnt_add_to_ns+0x322/0x890
attach_recursive_mnt.isra.0+0xf2a/0x1a00
path_mount+0x139c/0x1d40
This needs a mount with MNT_SHRINKABLE to bind from. That's what
finish_automount() creates (submounts of NFS, AFS and CIFS and the
tracefs mount below debugfs). Bind mounts inherit the flag. A mount
namespace with a FAN_MARK_MNTNS mark does the rest and root in a user
namespace can have both.
Initialize to_notify in alloc_vfsmnt() and leave a mount alone that is
queued already. mnt_notify() looks at the state the mount has when the
list is drained so a single entry per mount is enough. The move event
for a mount that is unmounted under the same hold is lost. That's fine.
The detach is what matters.
-
CVE-2026-98990
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: check a submount for references right before unmounting it
shrink_submounts() and mark_mounts_for_expiry() first collect all the
mounts they are allowed to unmount and then unmount them.
Whether a mount is busy is decided by propagate_mount_busy() on the
tree. But unmounting the first mount changes the tree that the second
one propagates into. propagate_umount()
moves a surviving overmount off a copy it unmounts and mounts it where
the copy was mounted. If that's where the propagated copy of the second
victim is looked up the overmount becomes a candidate of the second
umount_tree(). It's childless and so trim_one() commits it without
looking at its reference count.
So a synchronous umount pulls out a busy mount that is in use somewhere
else and marks it MNT_SYNC_UMOUNT while it has users:
umount2(/tmp/plshrink/p1, 0) = 0 errno 0
cwd is (unreachable)
The same two umounts requested one after the other fail with EBUSY.
This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of
NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts
inherit the flag.
Check each mount right before it is unmounted under the same hold of
namespace_sem and mount_lock as the umount itself. Make sure that the
algorithm stays linear.
-
CVE-2026-98989
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: check a recursive bind mount for mount namespace loops
do_loopback() refuses to bind mount the file of a mount namespace that
is as old as the caller's or older because a mount namespace that holds
a mount of its own file, or of an ancestor's, would cause a cycle. But
it only checks the dentry the bind mount starts from. With MS_REC
everything below it is copied and do_loopback() passes
CL_COPY_MNT_NS_FILE so mount namespace files below the source are
copied.
That's fine for a source in the caller's own mount namespace. Every
mount namespace file in there passed the same check when it was
bind-mounted. It isn't fine for a source in another mount namespace.
may_copy_tree() accepts a bind mount of any nsfs or pidfs file no matter
what mount namespace it lives in so that /proc/pid/ns/ and pidfds
can be bind mounted. If we create a bind-mount stack of mount namespaces
file descriptors the kernel will copy them irrespective of their
ancestoral relationship to the mount namespace in question:
151 146 0:7 net:[4026531833] /tmp/nrc/y rw - nsfs nsfs rw
152 151 0:7 mnt:[4026532293] /tmp/nrc/y rw - nsfs nsfs rw
Mount 152 is a mount of the mount namespace file of mount namespace
4026532293 inside mount namespace 4026532293. That namespace and every
mount in it are leaked... All it takes is a process in an older mount
namespace that stacks the file and repeating it leaks without limit:
after control: Shmem: 380 kB
child: mount(/proc/self/fd/6, MS_BIND|MS_REC): ok
after cycle: Shmem: 65916 kB
do_move_mount() runs check_for_nsfs_mounts() over a detached tree for
exactly that reason. Do the same for the copy before it is grafted.
-
CVE-2026-98988
•
published on October 23, 2026
In the Linux kernel, the following vulnerability has been resolved:
namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE
open_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a
copy of the tree at the given path. The caller needs to be privileged
over its current user namespace because the new mount namespace will be
owned by it. It doesn't need to be privileged over the mount namespace
the tree is copied from. An unprivileged user just needs to create a
user namespace first.
The copy follows the rules of a detached bind mount. Without
AT_RECURSIVE only the mount itself is cloned and its children are left
out. With AT_RECURSIVE unbindable mounts are skipped. Both is fine when
the caller has privileges over the source mount namespace because it
could unmount those mounts anyway. Not so for an unprivileged user in
that mount namespace. For them a mount namespace copy is what unshare()
does. copy_mnt_ns() copies everything including unbindable mounts and
lock_mnt_tree() makes sure nothing can be unmounted in the copy. Nothing
that was covered gets revealed.
create_new_namespace() only does the locking and so the covered content
is right there in the new mount namespace:
# mount -t tmpfs none /tmp/otn; mkdir /tmp/otn/covered
# echo hidden /tmp/otn/covered/under.txt
# mount -t tmpfs none /tmp/otn/covered
uid 1000, after unshare(CLONE_NEWUSER):
fd = open_tree(AT_FDCWD, "/tmp/otn", OPEN_TREE_NAMESPACE);
setns(fd, CLONE_NEWNS);
open("/covered/under.txt", O_RDONLY) -> "hidden"
Covering paths with mounts is how container runtimes mask parts of
/proc and /sys and how admins hide things.
When the caller's user namespace doesn't own the source mount namespace
copy the way unshare() does and refuse a non-recursive copy of a mount
that has anything mounted below the requested directory and copy
unbindable mounts in a recursive copy. A caller that is privileged over
the source mount namespace sees no change.
