6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Göttsche commit 1ca924044bf0de879a1648be93a56939652267d3 upstream. 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 Signed-off-by: Greg Kroah-Hartman --- security/selinux/avc.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/security/selinux/avc.c +++ b/security/selinux/avc.c @@ -578,7 +578,7 @@ static int avc_latest_notif_update(u32 s } } 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 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); }