netdev - [PATCH bpf] xsk: fix refcount underflow in error path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230809142843.13944-1-magnus.karlsson@gmail.com>
Date: Wed,  9 Aug 2023 16:28:43 +0200
From: Magnus Karlsson <magnus.karlsson@...il.com>
To: magnus.karlsson@...el.com,
	bjorn@...nel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	netdev@...r.kernel.org,
	maciej.fijalkowski@...el.com
Cc: jonathan.lemon@...il.com,
	bpf@...r.kernel.org,
	syzbot+8ada0057e69293a05fd4@...kaller.appspotmail.com
Subject: [PATCH bpf] xsk: fix refcount underflow in error path

From: Magnus Karlsson <magnus.karlsson@...el.com>

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@...kaller.appspotmail.com
Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
---
 net/xdp/xsk.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index b89adb52a977..10ea85c03147 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -994,6 +994,7 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
 				err = xp_alloc_tx_descs(xs->pool, xs);
 				if (err) {
 					xp_put_pool(xs->pool);
+					xs->pool = NULL;
 					sockfd_put(sock);
 					goto out_unlock;
 				}

base-commit: 999f6631866e9ea81add935b9c6ebaab0579d259
-- 
2.34.1