From 1ca924044bf0de879a1648be93a56939652267d3 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Christian=20G=C3=B6ttsche?= Date: Wed, 23 Sep 2026 12:13:23 +0200 Subject: [PATCH] selinux: fix data race on AVC latest_notif MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit avc_policy_seqno() reads latest_notif without holding notif_lock, while avc_latest_notif_update() can update it under that lock. KCSAN reports these concurrent accesses during policy boolean updates and permission checks. Use READ_ONCE() for the lockless read and WRITE_ONCE() for the update. The spinlock continues to serialize the comparison and update against other writers. Reads made while holding notif_lock cannot race with a writer and can remain plain accesses. This marks both sides of the intentional concurrent access and constrains compiler transformations, without suppressing checking with data_race(). Cc: stable@vger.kernel.org Fixes: 788e7dd4c22e ("SELinux: Improve read/write performance") Reported-by: syzbot+a7f7cb0737bd91aa698c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=a7f7cb0737bd91aa698c Signed-off-by: Christian Göttsche Acked-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/avc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/security/selinux/avc.c b/security/selinux/avc.c index 560a82c6d682..b91f914d292e 100644 --- a/security/selinux/avc.c +++ b/security/selinux/avc.c @@ -578,7 +578,7 @@ static int avc_latest_notif_update(u32 seqno, int is_insert) } } else { if (seqno > selinux_avc.avc_cache.latest_notif) - selinux_avc.avc_cache.latest_notif = seqno; + WRITE_ONCE(selinux_avc.avc_cache.latest_notif, seqno); } spin_unlock_irqrestore(¬if_lock, flag); @@ -1206,5 +1206,6 @@ int avc_has_perm(u32 ssid, u32 tsid, u16 tclass, u32 avc_policy_seqno(void) { - return selinux_avc.avc_cache.latest_notif; + /* Writers hold notif_lock; readers only sample the sequence number. */ + return READ_ONCE(selinux_avc.avc_cache.latest_notif); }