posix-cpu-timers: Prevent UAF caused by non-leader exec() race

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-64560
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-29 17:16:53 UTC
Updated2026-07-30 12:19:03 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: posix-cpu-timers: Prevent UAF caused by non-leader exec() race Wongi and Jungwoo decoded and reported a non-leader exec() related race which can result in an UAF: sys_timer_delete() exec() posix_cpu_timer_del() // Observes old leader p = pid_task(pid, pid_type); de_thread() switch_leader(); release_task(old_leader) __exit_signal(old_leader) sighand = lock(old_leader, sighand); posix_cpu_timers*_exit(); sighand = lock_task_sighand(p) unhash_task(old_leader); sh = lock(p, sighand) old_leader->sighand = NULL; unlock(sighand); (p->sighand == NULL) unlock(sh) return NULL; // Returns without action if(!sighand) return 0; free_posix_timer(); This is "harmless" unless the deleted timer was armed and enqueued in p->signal because on exec() a TGID targeted timer is inherited. As sys_timer_delete() freed the underlying posix timer object run_posix_cpu_timers() or any timerqueue related add/delete operations on other timers will access the freed object's timerqueue node, which results in an UAF. There is a similar problem vs. posix_cpu_timer_set(). For regular posix timers it just transiently returns -ESRCH to user space, but for the use case in do_cpu_nanosleep() it's the same UAF just that the k_itimer is allocated on the stack. Also posix_cpu_timer_rearm() fails to rearm the timer, which means it stops to expire. While debating solutions Frederic pointed out another problem: posix_cpu_timer_del(tmr) __exit_signal(p) posix_cpu_timers*_exit(p); unhash_task(p); p->sighand = NULL; sh = lock_task_sighand(p) sighand = p->sighand; if (!sighand) return NULL; lock(sighand); if (!sh) WARN_ON_ONCE(timer_queued(tmr)); On weakly ordered architectures it is not guaranteed that posix_cpu_timer_del() will observe the stores in posix_cpu_timers*_exit() when p->sighand is observed as NULL, which means the WARN() can be a false positive. Solve these issues by: 1) Changing the store in __exit_signal() to smp_store_release(). 2) Adding a smp_acquire__after_ctrl_dep() into the !sighand path of lock_task_sighand(). 3) Creating a helper function for looking up the task and locking sighand which does not return when sighand == NULL. Instead it retries the task lookup and only if that fails it gives up. 4) Using that helper in the three affected functions. #1/#2 ensures that the reader side which observes sighand == NULL also observes all preceeding stores, i.e. the stores in posix_cpu_timers*_exit() and the ones in unhash_task(). #3 ensures that the above described non-leader exec() situation is handled gracefully. When the task lookup returns the old leader, but sighand == NULL then it retries. In the non-leader exec() case the subsequent task lookup will observe the new leader due to #1/#2. In normal exit() scenarios the subsequent lookup fails. When the task lookup fails, the function also checks whether the timer is still enqueued and issues a warning if that's the case. Unfortunately there is nothing which can be done about it, but as the task is already not longer visible the timer should not be accessed anymore. This check also requires memory ordering, which is not provided when the first lookup fails. To achieve that the check is preceeded by a smp_rmb() which pairs with the smp_wmb() in write_seqlock() in __exit_signal(). That ensures that the stores in posix_cpu_timers*_exit() are visible. The history of the non-leader exec() issue goes back to the early days of posix CPU timers, which stored a pointer to the group leader task in the timer. That obviously fails when a non-leader exec() switches the leader. commit e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec") added a temporary workaround for that in 2010 which surv ---truncated---

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.001120000 probability, percentile 0.016040000 (date 2026-07-30)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 67aa823e3e8c229c6d374df79c804f6721cb83b6 git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 d8bcb28abad857f1415da7656f19b2ada90af04f git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 cc35ddbc497311e0b6b9a6a6a4f4d1217d6ab1aa git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 12a891c773aeb5823d63dbd0cb2ab931d6c21c9b git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 e74443f5db0037c556ef436fa64b88bf4ea08f83 git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 6a7ecc25abe6f0fecc6e62a05096987200edbd02 git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 ad1cafa1bdaa71da85d71cac053838bbe97852b6 git Not specified
CNA Linux Linux affected 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 920f893f735e92ba3a1cd9256899a186b161928d git Not specified
CNA Linux Linux affected 5.7 Not specified
CNA Linux Linux unaffected 5.7 semver Not specified
CNA Linux Linux unaffected 5.10.262 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.213 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.180 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.147 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.100 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.41 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.5 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/920f893f735e92ba3a1cd9256899a186b161928d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6a7ecc25abe6f0fecc6e62a05096987200edbd02 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d8bcb28abad857f1415da7656f19b2ada90af04f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e74443f5db0037c556ef436fa64b88bf4ea08f83 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ad1cafa1bdaa71da85d71cac053838bbe97852b6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cc35ddbc497311e0b6b9a6a6a4f4d1217d6ab1aa 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/67aa823e3e8c229c6d374df79c804f6721cb83b6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/12a891c773aeb5823d63dbd0cb2ab931d6c21c9b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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