CVE-2026-63827

In the Linux kernel, the following vulnerability has been resolved: apparmor: fix use-after-free in rawdata dedup loop aa_replace_profiles() walks ns->rawdata_list to dedup the incoming policy blob against entries already attached to existing profiles. Per the kernel-doc on struct aa_loaddata, list membership does not hold a reference: profiles hold pcount, and when the last pcount drops, do_ploaddata_rmfs() is queued on a workqueue that takes ns->lock and removes the entry. Between dropping the last pcount and the workqueue running, an entry remains on the list with pcount == 0. aa_get_profile_loaddata() is an unconditional kref_get() on pcount, so when the dedup loop hits such an entry, refcount hardening reports refcount_t: addition on 0; use-after-free. inside aa_replace_profiles(), and the poisoned counter then trips "saturated" and "underflow" warnings on the subsequent uses of the same loaddata. Before commit a0b7091c4de4 ("apparmor: fix race on rawdata dereference") the dedup path used a get_unless_zero-style helper on a single counter, so the existing "if (tmp)" guard was meaningful. The split-refcount refactor introduced aa_get_profile_loaddata(), which has plain kref_get() semantics, and the guard quietly became a no-op. Introduce aa_get_profile_loaddata_not0(), matching the existing _not0 convention used by aa_get_profile_not0(), and use it for the rawdata_list dedup lookup so dying entries are skipped. Reproduced on x86_64 with v7.1-rc5 in QEMU+KVM running Ubuntu 24.04 + stress-ng 0.17.06: stress-ng --apparmor 1 --klog-check --timeout 60s Without this patch the three refcount_t warnings fire within a few seconds. With it the same 60 s run is clean. Coverage is a smoke-test only; a longer soak with CONFIG_KASAN, CONFIG_KCSAN and CONFIG_PROVE_LOCKING would be welcome from anyone with the cycles.

• https://git.kernel.org/stable/c/15fd83a1e42ede15070968806bb6c8b1a5170688
• https://git.kernel.org/stable/c/5e34fa9f6f7cd688ae153fff13139a5cf2d42339
• https://git.kernel.org/stable/c/643221da57dbb1a8fd800610331cf1ec27969f71
• https://git.kernel.org/stable/c/6f060496d03e4dc560a40f73770bd08335cb7a27
• https://git.kernel.org/stable/c/a7a2890028f16e5b0af0bb005d80fcb32559cca3
• https://git.kernel.org/stable/c/b17f0c59cc1525765625cf07d0391b7f9c1ed7e5
• https://git.kernel.org/stable/c/c3ca2631073b2cef06824fd2bfc452ff7a1023de
• https://git.kernel.org/stable/c/ce261a20b41db522e320a41bbf1292bf85af66df

Published

Jul 19, 2026

Last Modified

Jul 27, 2026

Status

Awaiting Analysis

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