From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BF79D2E2840 for ; Mon, 24 Nov 2025 20:59:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764017960; cv=none; b=gmi4q3eEkxvldVpqCcojT+MVAjETNGW4JvhcEJMHNq0vJXYqTojdlaV4KlWAuqhWyUBBIwF82/UWeoD1iOTEHFrpb5OxGtC2Eg+EGroS5HDxcflUIKi9xy3msT6X/davWBpWdAQiJ3Tm7yE2r5uVdd02+uMoXU5U2T2PPivZBVQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764017960; c=relaxed/simple; bh=RNJVZtLuB6fBQQX3bg+HvE5t6eC0q9iMziGBjtzsGTM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RINesUn8tQBdCqhHsVgSZ7sleRP7pVpo50JV1Fkrb3gmyzM5Af8bkX7CmVOS6OnplzRwnUEj9YNCWzZHV/YGw0OCVBkndZNKjbnpUFniRxR+gm0R8D77VPbslZZ5N0bqSvisdd4X08/iBwG4UzYsx96HAFB2C5izgz90PATZzK4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nHXqkXrZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nHXqkXrZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7F42C16AAE; Mon, 24 Nov 2025 20:59:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764017960; bh=RNJVZtLuB6fBQQX3bg+HvE5t6eC0q9iMziGBjtzsGTM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nHXqkXrZkiqK8ed1w2eIvO7ERCIRAM5PSCZcEzaPYfiEdUMnFn8bSmpC23+9VNDk9 +YXZplWQmhZqI1yf7MwGB+XHyf6ceDZXWQ/XHv7rH14V4itOB8qoB9snO70jvDLIqr Dve+7P865K2/Baxv+j2MILIUVPStnG1bIxh4l2EwN3WNzT58jDiJAwUWMJBPVJzNFv HUfhtY97BOQs0JYOFdYUDkyVym6DS5BBs5VRlf3i2EmmOTBVEj0tTbF1Ez5cYzyZ45 36Zv8ez0h7w0wDqleXZy7VmB+QWibgs2kMl3ri5K4By/K/ATLcyU8pcSOJg+IwJabC 65k/h4cj3r+mw== From: Sasha Levin To: stable@vger.kernel.org Cc: Eric Dumazet , syzbot+355158e7e301548a1424@syzkaller.appspotmail.com, "Matthieu Baerts (NGI0)" , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.10.y 2/2] mptcp: fix race condition in mptcp_schedule_work() Date: Mon, 24 Nov 2025 15:59:17 -0500 Message-ID: <20251124205917.27437-2-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251124205917.27437-1-sashal@kernel.org> References: <2025112402-confiding-slideshow-217f@gregkh> <20251124205917.27437-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Eric Dumazet [ Upstream commit 035bca3f017ee9dea3a5a756e77a6f7138cc6eea ] syzbot reported use-after-free in mptcp_schedule_work() [1] Issue here is that mptcp_schedule_work() schedules a work, then gets a refcount on sk->sk_refcnt if the work was scheduled. This refcount will be released by mptcp_worker(). [A] if (schedule_work(...)) { [B] sock_hold(sk); return true; } Problem is that mptcp_worker() can run immediately and complete before [B] We need instead : sock_hold(sk); if (schedule_work(...)) return true; sock_put(sk); [1] refcount_t: addition on 0; use-after-free. WARNING: CPU: 1 PID: 29 at lib/refcount.c:25 refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25 Call Trace: __refcount_add include/linux/refcount.h:-1 [inline] __refcount_inc include/linux/refcount.h:366 [inline] refcount_inc include/linux/refcount.h:383 [inline] sock_hold include/net/sock.h:816 [inline] mptcp_schedule_work+0x164/0x1a0 net/mptcp/protocol.c:943 mptcp_tout_timer+0x21/0xa0 net/mptcp/protocol.c:2316 call_timer_fn+0x17e/0x5f0 kernel/time/timer.c:1747 expire_timers kernel/time/timer.c:1798 [inline] __run_timers kernel/time/timer.c:2372 [inline] __run_timer_base+0x648/0x970 kernel/time/timer.c:2384 run_timer_base kernel/time/timer.c:2393 [inline] run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403 handle_softirqs+0x22f/0x710 kernel/softirq.c:622 __do_softirq kernel/softirq.c:656 [inline] run_ktimerd+0xcf/0x190 kernel/softirq.c:1138 smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 Cc: stable@vger.kernel.org Fixes: 3b1d6210a957 ("mptcp: implement and use MPTCP-level retransmission") Reported-by: syzbot+355158e7e301548a1424@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6915b46f.050a0220.3565dc.0028.GAE@google.com/T/#u Signed-off-by: Eric Dumazet Reviewed-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20251113103924.3737425-1-edumazet@google.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/mptcp/protocol.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 591882cf86453..e40cd7f61106a 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -716,14 +716,19 @@ static void mptcp_reset_timer(struct sock *sk) bool mptcp_schedule_work(struct sock *sk) { - if (inet_sk_state_load(sk) != TCP_CLOSE && - schedule_work(&mptcp_sk(sk)->work)) { - /* each subflow already holds a reference to the sk, and the - * workqueue is invoked by a subflow, so sk can't go away here. - */ - sock_hold(sk); + if (inet_sk_state_load(sk) == TCP_CLOSE) + return false; + + /* Get a reference on this socket, mptcp_worker() will release it. + * As mptcp_worker() might complete before us, we can not avoid + * a sock_hold()/sock_put() if schedule_work() returns false. + */ + sock_hold(sk); + + if (schedule_work(&mptcp_sk(sk)->work)) return true; - } + + sock_put(sk); return false; } -- 2.51.0