GHSA-9X8R-8WJJ-JGJV
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31In 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)
{
"affected": [],
"aliases": [
"CVE-2026-97938"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:21Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nreboot: fix cad_pid use-after-free race\n\ncad_pid is a single kernel-wide struct pid pointer. proc_do_cad_pid()\nreads it and passes it to pid_vnr() without protecting the lifetime of\nthe referenced struct pid. A concurrent writer can replace cad_pid and\ndrop the final reference to the old struct pid after the reader has\nloaded the pointer but before pid_vnr() has finished dereferencing it,\ncausing a use-after-free.\n\nkill_cad_pid() has the same lifetime race when it passes cad_pid to\nkill_pid().\n\nAt the time this issue was reported, an unprivileged user could reach the\nsysctl through user and PID namespaces because cad_pid was registered in\npid_table[]. Moving cad_pid back to the global reboot sysctl table\ncorrected that namespace and permission mismatch, but did not fix the\nunderlying lifetime race.\n\nFix this by treating cad_pid as an RCU-protected pointer at both read\nsites and by waiting for a grace period before dropping the old reference\non the write side.\n\ncall_rcu(\u0026old_pid-\u003ercu, ...) cannot be used here because free_pid()\nalso queues pid-\u003ercu; queueing the same rcu_head twice can corrupt the\nRCU callback list.\n\nOriginal KASAN crash stack:\n kernel/pid.c:545 pid_nr_ns() # reads freed pid-\u003elevel\n kernel/pid.c:556 pid_vnr() # calls pid_nr_ns()\n kernel/pid.c:775 proc_do_cad_pid() # calls pid_vnr(cad_pid)",
"id": "GHSA-9x8r-8wjj-jgjv",
"modified": "2026-09-25T12:31:29Z",
"published": "2026-09-25T12:31:29Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97938"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5a88f78df753993469dab4d1831f8fb4256a9468"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9a17b0e053197a6a42cdc75e75a35b17aa662088"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ad72e2566643fff7f01666d845fb026898155e1f"
}
],
"schema_version": "1.4.0",
"severity": []
}
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