This is a note to let you know that I've just added the patch titled
xsk: fix refcount underflow in error path
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xsk-fix-refcount-underflow-in-error-path.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 85c2c79a07302fe68a1ad5cc449458cc559e314d Mon Sep 17 00:00:00 2001
From: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Date: Wed, 9 Aug 2023 16:28:43 +0200
Subject: xsk: fix refcount underflow in error path
From: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
commit 85c2c79a07302fe68a1ad5cc449458cc559e314d upstream.
Fix a refcount underflow problem reported by syzbot that can happen
when a system is running out of memory. If xp_alloc_tx_descs() fails,
and it can only fail due to not having enough memory, then the error
path is triggered. In this error path, the refcount of the pool is
decremented as it has incremented before. However, the reference to
the pool in the socket was not nulled. This means that when the socket
is closed later, the socket teardown logic will think that there is a
pool attached to the socket and try to decrease the refcount again,
leading to a refcount underflow.
I chose this fix as it involved adding just a single line. Another
option would have been to move xp_get_pool() and the assignment of
xs->pool to after the if-statement and using xs_umem->pool instead of
xs->pool in the whole if-statement resulting in somewhat simpler code,
but this would have led to much more churn in the code base perhaps
making it harder to backport.
Fixes: ba3beec2ec1d ("xsk: Fix possible crash when multiple sockets are created")
Reported-by: syzbot+8ada0057e69293a05fd4@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230809142843.13944-1-magnus.karlsson@xxxxxxxxx
Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/xdp/xsk.c | 1 +
1 file changed, 1 insertion(+)
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -1001,6 +1001,7 @@ static int xsk_bind(struct socket *sock,
err = xp_alloc_tx_descs(xs->pool, xs);
if (err) {
xp_put_pool(xs->pool);
+ xs->pool = NULL;
sockfd_put(sock);
goto out_unlock;
}
Patches currently in stable-queue which might be from magnus.karlsson@xxxxxxxxx are
queue-5.15/xsk-fix-refcount-underflow-in-error-path.patch
