CVE-2026-97938
UnknownSummary
A use-after-free race exists in the Linux kernel around the global cad_pid pointer. proc_do_cad_pid() and kill_cad_pid() use cad_pid without protecting the lifetime of the referenced struct pid, so a concurrent writer can drop the final reference to the old struct before the reader finishes dereferencing it. The fix treats cad_pid as an RCU-protected pointer and waits for a grace period before dropping the old reference.
Risk Assessment
Can cause kernel memory corruption, system crash (kernel panic), or potential privilege escalation by an unprivileged user who can reach the sysctl through user and PID namespaces.
Recommendation
Update the Linux kernel to a version containing the RCU fix for cad_pid. Until patched, restrict access to the relevant sysctl entries for unprivileged users.
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Original NVD description (English source)
In 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)
Vulnerability data from NVD (NIST) · CISA KEV · EPSS