reboot: fix cad_pid use-after-free race

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-97938
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 11:17:21 UTC
Updated2026-09-25 11:17:21 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: reboot: fix cad_pid use-after-free race cad_pid is a single kernel-wide struct pid pointer. proc_do_cad_pid() reads it and passes it to pid_vnr() without protecting the lifetime of the referenced struct pid. A concurrent writer can replace cad_pid and drop the final reference to the old struct pid after the reader has loaded the pointer but before pid_vnr() has finished dereferencing it, causing a use-after-free. kill_cad_pid() has the same lifetime race when it passes cad_pid to kill_pid(). At the time this issue was reported, an unprivileged user could reach the sysctl through user and PID namespaces because cad_pid was registered in pid_table[]. Moving cad_pid back to the global reboot sysctl table corrected that namespace and permission mismatch, but did not fix the underlying lifetime race. Fix this by treating cad_pid as an RCU-protected pointer at both read sites and by waiting for a grace period before dropping the old reference on the write side. call_rcu(&old_pid->rcu, ...) cannot be used here because free_pid() also queues pid->rcu; queueing the same rcu_head twice can corrupt the RCU callback list. Original KASAN crash stack: kernel/pid.c:545 pid_nr_ns() # reads freed pid->level kernel/pid.c:556 pid_vnr() # calls pid_nr_ns() kernel/pid.c:775 proc_do_cad_pid() # calls pid_vnr(cad_pid)

Risk And Classification

EPSS: 0.001980000 probability, percentile 0.085920000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 ad72e2566643fff7f01666d845fb026898155e1f git Not specified
CNA Linux Linux affected 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 9a17b0e053197a6a42cdc75e75a35b17aa662088 git Not specified
CNA Linux Linux affected 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 5a88f78df753993469dab4d1831f8fb4256a9468 git Not specified
CNA Linux Linux affected 2.6.19 Not specified
CNA Linux Linux unaffected 2.6.19 semver Not specified
CNA Linux Linux unaffected 6.18.53 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.7 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/9a17b0e053197a6a42cdc75e75a35b17aa662088 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5a88f78df753993469dab4d1831f8fb4256a9468 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ad72e2566643fff7f01666d845fb026898155e1f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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