From 640cf2f09575c9dc344b3f7be2498d31e3923ead Mon Sep 17 00:00:00 2001 From: Zhengmian Hu Date: Mon, 19 Jan 2026 19:03:07 -0500 Subject: [PATCH] apparmor: avoid per-cpu hold underflow in aa_get_buffer 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. Fixes: ea9bae12d028 ("apparmor: cache buffers on percpu list if there is lock contention") Signed-off-by: Zhengmian Hu Signed-off-by: John Johansen --- 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 8d5d9a966b71..9175fd677ef3 100644 --- a/security/apparmor/lsm.c +++ b/security/apparmor/lsm.c @@ -2137,7 +2137,8 @@ char *aa_get_buffer(bool in_atomic) if (!list_empty(&cache->head)) { aa_buf = 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]; -- 2.47.3