{"id":"CVE-2026-97903","summary":"exit: hold a reference to thread_pid across proc_flush_pid","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nexit: hold a reference to thread_pid across proc_flush_pid\n\nCommit 0a36bad01731 (\"release_task: kill the no longer needed\nget/put_pid(thread_pid)\") removed the reference around proc_flush_pid().\nIt assumed that free_pids(post.pids) at the end of release_task() would\nkeep thread_pid alive until then.\n\nThat assumption is wrong.  __change_pid() only records a detached PID in\npost.pids when pid_has_task() is false for every PIDTYPE.  If another task\nstill uses the exiting task's PID as its process group or session ID,\n__unhash_process() removes the exiting task's PIDTYPE_PID link but leaves\nthe PID out of post.pids.  release_task() therefore holds no reference to\nit after dropping tasklist_lock.\n\nThe other task can then remove the remaining PIDTYPE links.  Its\nfree_pids() call schedules delayed_put_pid(), and the RCU callback can free\nthe PID before the first release_task() reaches proc_flush_pid().\n\nAn unprivileged reproducer races wait4(-1) against setsid() to trigger this\nordering.  Three of three fresh v7.2 KASAN boots reported:\n\n    BUG: KASAN: slab-use-after-free in\n    proc_invalidate_siblings_dcache+0x3e2/0x3f0\n    Read of size 8 by task h7_pid_reaper/1921\n\n    Call Trace:\n     proc_invalidate_siblings_dcache\n     release_task\n     wait_consider_task\n     __do_wait\n     do_wait\n     kernel_wait4\n\n    Freed by task 0:\n     kmem_cache_free\n     put_pid\n     delayed_put_pid\n     rcu_core\n\n    Last potentially related work creation:\n     __call_rcu_common\n     free_pids\n     ksys_setsid\n\nKASAN identified a 144-byte object from the pid cache and located the bad\nread 80 bytes into the freed object, matching pid-\u003einodes.  With an\nexplicit reference, three of three fresh boots completed without a KASAN\nreport.  The concurrent RCU callback dropped its reference while\nproc_flush_pid() was protected, and the balancing put_pid() performed the\nfinal free afterward.\n\nTake a reference before __unhash_process() clears p-\u003ethread_pid and release\nit after proc_flush_pid() completes.\n\nA tested source reproducer is available privately on request.  No\ncontrolled read or write, information leak, or privilege escalation is\nclaimed.  The mainline patch applies directly to v6.19.y and newer;\nv6.16.y through v6.18.y need a context-adjusted backport.","modified":"2026-09-27T03:47:38.647154344Z","published":"2026-09-25T10:22:29.852Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97903.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/96803a12e8ac15f0a1b4b151db59038f12304e58"},{"type":"WEB","url":"https://git.kernel.org/stable/c/bcb0936862f2b653114d9bd582ca26990ef54a64"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cdd812d0683dee14ead02c9eded568685e61b23f"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/97xxx/CVE-2026-97903.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-97903"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"0a36bad01731e71568bdd365764d38b6bd576ab0"},{"fixed":"bcb0936862f2b653114d9bd582ca26990ef54a64"},{"fixed":"96803a12e8ac15f0a1b4b151db59038f12304e58"},{"fixed":"cdd812d0683dee14ead02c9eded568685e61b23f"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97903.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.16.0"},{"fixed":"6.18.53"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.7"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-97903.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}