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Mon, 19 Jan 2026 16:03:33 -0800 (PST) From: Zhengmian Hu To: john.johansen@canonical.com, john@apparmor.net, apparmor@lists.ubuntu.com Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Zhengmian Hu Subject: [PATCH v2 1/1] apparmor: avoid per-cpu hold underflow in aa_get_buffer Date: Mon, 19 Jan 2026 19:03:07 -0500 Message-ID: <20260120000307.369587-2-huzhengmian@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260120000307.369587-1-huzhengmian@gmail.com> References: <20260120000307.369587-1-huzhengmian@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When aa_get_buffer() pulls from the per-cpu list it unconditionally decrements cache->hold. If hold reaches 0 while count is still non-zero, the unsigned decrement wraps to UINT_MAX. This keeps hold non-zero for a very long time, so aa_put_buffer() never returns buffers to the global list, which can starve other CPUs and force repeated kmalloc(aa_g_path_max) allocations. Guard the decrement so hold never underflows. Signed-off-by: Zhengmian Hu --- security/apparmor/lsm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c index 9b6c2f157..a6c884ba6 100644 --- a/security/apparmor/lsm.c +++ b/security/apparmor/lsm.c @@ -1868,7 +1868,8 @@ char *aa_get_buffer(bool in_atomic) if (!list_empty(&cache->head)) { aa_buf =3D list_first_entry(&cache->head, union aa_buffer, list); list_del(&aa_buf->list); - cache->hold--; + if (cache->hold) + cache->hold--; cache->count--; put_cpu_ptr(&aa_local_buffers); return &aa_buf->buffer[0]; --=20 2.52.0