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 0A71235A957; Wed, 3 Dec 2025 16:41:04 +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=1764780064; cv=none; b=qLL5X/rJPZx0nSeJikz3eRCC6GB1pd3tmPg4fV65tq3gYnyw6aNDycXxHFBKzPdvSva4lKsg/n/ZesTqs6XT3lJbsPy/jG303WTgYKlwp3i2HJUghw0qw2moSppa4MrA41UjRQVVVb2bpDyxJIeqXXfqRXbBGHXukxKujpeKBYA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764780064; c=relaxed/simple; bh=P0mmfrR0EkVZSLAp3GFc0i6ibJ3NLEAiSX7vG8wPUP0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DPiA3jgHluM7s21OrL8YWUcWAE6juIllEwRaa8fryBzpDeB3WZG+bIrTvSj+jQDxmjZ3TIBKIPyW4hQkt9TROF4N2E40F7xkSJxdzTn9XlEwjxhCudeacAzGZS25C7jj1yoJNYh6cEmQnccX/SeRYerM9jQ617g3dBfvpl3aL+s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=CUw0wxbg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="CUw0wxbg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6D145C4CEF5; Wed, 3 Dec 2025 16:41:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1764780063; bh=P0mmfrR0EkVZSLAp3GFc0i6ibJ3NLEAiSX7vG8wPUP0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CUw0wxbgW+K7tAw7YbuTyp+ERM0NXBDP+Wfnv0RnL+tnuv20slhbMxSSnYGoRItud 9gLK+2ne5YkJ5Dkr3XWoRSJy9web+QgG3PNUwxnGCDE2gfo63L8MTy0C3wRK8x6+aE z10RmCQs2YDtR0KycY1iLQyMYC/cPKmNPnQFFSQI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+355158e7e301548a1424@syzkaller.appspotmail.com, Eric Dumazet , "Matthieu Baerts (NGI0)" , Jakub Kicinski Subject: [PATCH 6.1 444/568] mptcp: fix race condition in mptcp_schedule_work() Date: Wed, 3 Dec 2025 16:27:26 +0100 Message-ID: <20251203152456.962176679@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20251203152440.645416925@linuxfoundation.org> References: <20251203152440.645416925@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet commit 035bca3f017ee9dea3a5a756e77a6f7138cc6eea upstream. 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: Greg Kroah-Hartman --- net/mptcp/protocol.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -966,14 +966,19 @@ static void mptcp_reset_rtx_timer(struct 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; }