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Hallyn" , Georgia Garcia , Cengiz Can , Colin Ian King , apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] apparmor: fix use-after-free in rawdata dedup loop Date: Tue, 26 May 2026 00:04:46 +0200 Message-ID: <20260525220446.975352-1-linuxoid@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Fixes: a0b7091c4de4 ("apparmor: fix race on rawdata dereference") Reported-by: Colin Ian King Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221513 Cc: stable@vger.kernel.org Signed-off-by: Ruslan Valiyev --- security/apparmor/include/policy_unpack.h | 19 +++++++++++++++++++ security/apparmor/policy.c | 8 ++++++-- 2 files changed, 25 insertions(+), 2 deletions(-) diff --git a/security/apparmor/include/policy_unpack.h b/security/apparmor/include/policy_unpack.h index e5a95dc4da1f..b9de0fdf9ee5 100644 --- a/security/apparmor/include/policy_unpack.h +++ b/security/apparmor/include/policy_unpack.h @@ -163,6 +163,25 @@ aa_get_profile_loaddata(struct aa_loaddata *data) return data; } +/** + * aa_get_profile_loaddata_not0 - get a profile reference count if not zero + * @data: reference to get a count on + * + * Like aa_get_profile_loaddata(), but safe to call on an entry that may + * be on a list (e.g. ns->rawdata_list) where the last pcount has already + * dropped and the deferred cleanup has not yet run. + * + * Returns: pointer to reference, or %NULL if @data is NULL or its + * profile refcount has already reached zero. + */ +static inline struct aa_loaddata * +aa_get_profile_loaddata_not0(struct aa_loaddata *data) +{ + if (data && kref_get_unless_zero(&data->pcount)) + return data; + return NULL; +} + void __aa_loaddata_update(struct aa_loaddata *data, long revision); bool aa_rawdata_eq(struct aa_loaddata *l, struct aa_loaddata *r); void aa_loaddata_kref(struct kref *kref); diff --git a/security/apparmor/policy.c b/security/apparmor/policy.c index b6a5eb4021db..e103cce6f4af 100644 --- a/security/apparmor/policy.c +++ b/security/apparmor/policy.c @@ -1223,8 +1223,12 @@ ssize_t aa_replace_profiles(struct aa_ns *policy_ns, struct aa_label *label, if (aa_rawdata_eq(rawdata_ent, udata)) { struct aa_loaddata *tmp; - tmp = aa_get_profile_loaddata(rawdata_ent); - /* check we didn't fail the race */ + /* + * Entries remain on rawdata_list with + * pcount == 0 until do_ploaddata_rmfs() + * runs; only take a live profile ref. + */ + tmp = aa_get_profile_loaddata_not0(rawdata_ent); if (tmp) { aa_put_profile_loaddata(udata); udata = tmp; base-commit: e7ae89a0c97ce2b68b0983cd01eda67cf373517d -- 2.43.0