FAILED: patch "[PATCH] selinux: fix data race on AVC latest_notif" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 1ca924044bf0de879a1648be93a56939652267d3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026101222-xbox-operate-40df@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1ca924044bf0de879a1648be93a56939652267d3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20G=C3=B6ttsche?= <[email protected]>
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().

index 560a82c6d682..b91f914d292e 100644
@@ -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(&notif_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);
 }

From: Christian Göttsche <[email protected]>

[ Upstream commit 1ca924044bf0de879a1648be93a56939652267d3 ]

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().

---
 security/selinux/avc.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index dcc8e1df4d7c5..e26f9b01b7305 100644
@@ -589,7 +589,7 @@ static int avc_latest_notif_update(struct selinux_avc *avc,
 		}
 	} else {
 		if (seqno > avc->avc_cache.latest_notif)
-			avc->avc_cache.latest_notif = seqno;
+			WRITE_ONCE(avc->avc_cache.latest_notif, seqno);
 	}
 	spin_unlock_irqrestore(&notif_lock, flag);
 

@@ -1202,7 +1202,8 @@ int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass,
 
 u32 avc_policy_seqno(struct selinux_state *state)
 {
-	return state->avc->avc_cache.latest_notif;
+	/* Writers hold notif_lock; readers only sample the sequence number. */
+	return READ_ONCE(state->avc->avc_cache.latest_notif);
 }
 
 void avc_disable(void)

2.53.0