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 773B018B0A; Wed, 25 Feb 2026 01:34:58 +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=1771983298; cv=none; b=sQ/r8cSvCrVUbYBSKzjwLZixZtNlsYXSOZ4xuOR1gmtBC1uGdHArD4k2tY874LnGDNEFwjvemYAwE3g5SbtxLHzG9MmfDL5yGHzD5EpIuvghuYhYfKCNypA4u1CmYasSnXzhnPdC348fp4wQ34tIcIU7PVP6By6L3IZ1mMhS+s8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771983298; c=relaxed/simple; bh=xjK0XPtmbEtXoxlbUvaEaMHcizM0X/B3164r3yo8bkQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rBWx4+aBsCuW6RcYayS7p3TS2mOVIwzrYS2qS35qEElZgS4lcM5ubv2poaqs95dudUjuw0n48fTZJ9Ipr00CAAmhby10zsulNnOcituSl742IL/5XPRqIDWN6CdClYGdCU3X5p3Uu5i7bFo1O3NAZ5nuJZvYAILYNyz1E0tumPQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=oy6KApnE; 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="oy6KApnE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F886C116D0; Wed, 25 Feb 2026 01:34:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1771983298; bh=xjK0XPtmbEtXoxlbUvaEaMHcizM0X/B3164r3yo8bkQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oy6KApnEHxDhADUfyqIlKqiDNeVUaFA7xIWfc1cg7PH5qQEoiEd1Hha7D9jA6ZDNF FGKtkjoArOXwNeArsinem3ww1VUkKcxwO4l/sBLhd3DaVwFMrFdNvG2GGX4OnH2M9O ZqUYA8KlOPK+XmKJgCfE7HZn7ykzHDGLPoUYpznk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+827272712bd6d12c79a4@syzkaller.appspotmail.com, Jiayuan Chen , Jijie Shao , Paolo Abeni , Sasha Levin Subject: [PATCH 6.19 431/781] serial: caif: fix use-after-free in caif_serial ldisc_close() Date: Tue, 24 Feb 2026 17:19:00 -0800 Message-ID: <20260225012410.270197394@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260225012359.695468795@linuxfoundation.org> References: <20260225012359.695468795@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit 308e7e4d0a846359685f40aade023aee7b27284c ] There is a use-after-free bug in caif_serial where handle_tx() may access ser->tty after the tty has been freed. The race condition occurs between ldisc_close() and packet transmission: CPU 0 (close) CPU 1 (xmit) ------------- ------------ ldisc_close() tty_kref_put(ser->tty) [tty may be freed here] <-- race window --> caif_xmit() handle_tx() tty = ser->tty // dangling ptr tty->ops->write() // UAF! schedule_work() ser_release() unregister_netdevice() The root cause is that tty_kref_put() is called in ldisc_close() while the network device is still active and can receive packets. Since ser and tty have a 1:1 binding relationship with consistent lifecycles (ser is allocated in ldisc_open and freed in ser_release via unregister_netdevice, and each ser binds exactly one tty), we can safely defer the tty reference release to ser_release() where the network device is unregistered. Fix this by moving tty_kref_put() from ldisc_close() to ser_release(), after unregister_netdevice(). This ensures the tty reference is held as long as the network device exists, preventing the UAF. Note: We save ser->tty before unregister_netdevice() because ser is embedded in netdev's private data and will be freed along with netdev (needs_free_netdev = true). How to reproduce: Add mdelay(500) at the beginning of ldisc_close() to widen the race window, then run the reproducer program [1]. Note: There is a separate deadloop issue in handle_tx() when using PORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper serial backend). This deadloop exists even without this patch, and is likely caused by inconsistency between uart_write_room() and uart_write() in serial core. It has been addressed in a separate patch [2]. KASAN report: ================================================================== BUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620 Read of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929 Call Trace: dump_stack_lvl+0x10e/0x1f0 print_report+0xd0/0x630 kasan_report+0xe4/0x120 handle_tx+0x5d1/0x620 dev_hard_start_xmit+0x9d/0x6c0 __dev_queue_xmit+0x6e2/0x4410 packet_xmit+0x243/0x360 packet_sendmsg+0x26cf/0x5500 __sys_sendto+0x4a3/0x520 __x64_sys_sendto+0xe0/0x1c0 do_syscall_64+0xc9/0xf80 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f615df2c0d7 Allocated by task 9930: Freed by task 64: Last potentially related work creation: The buggy address belongs to the object at ffff8881131e1000 which belongs to the cache kmalloc-cg-2k of size 2048 The buggy address is located 1168 bytes inside of freed 2048-byte region [ffff8881131e1000, ffff8881131e1800) The buggy address belongs to the physical page: page_owner tracks the page as allocated page last free pid 9778 tgid 9778 stack trace: Memory state around the buggy address: ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== [1]: https://gist.github.com/mrpre/f683f244544f7b11e7fa87df9e6c2eeb [2]: https://lore.kernel.org/linux-serial/20260204074327.226165-1-jiayuan.chen@linux.dev/T/#u Reported-by: syzbot+827272712bd6d12c79a4@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000a4a7550611e234f5@google.com/T/ Fixes: 56e0ef527b18 ("drivers/net: caif: fix wrong rtnl_is_locked() usage") Reviewed-by: Greg Kroah-Hartman Signed-off-by: Jiayuan Chen Reviewed-by: Jijie Shao Link: https://patch.msgid.link/20260206074450.154267-1-jiayuan.chen@linux.dev Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- drivers/net/caif/caif_serial.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/net/caif/caif_serial.c b/drivers/net/caif/caif_serial.c index c398ac42eae90..b90890030751f 100644 --- a/drivers/net/caif/caif_serial.c +++ b/drivers/net/caif/caif_serial.c @@ -284,6 +284,7 @@ static void ser_release(struct work_struct *work) { struct list_head list; struct ser_device *ser, *tmp; + struct tty_struct *tty; spin_lock(&ser_lock); list_replace_init(&ser_release_list, &list); @@ -292,9 +293,11 @@ static void ser_release(struct work_struct *work) if (!list_empty(&list)) { rtnl_lock(); list_for_each_entry_safe(ser, tmp, &list, node) { + tty = ser->tty; dev_close(ser->dev); unregister_netdevice(ser->dev); debugfs_deinit(ser); + tty_kref_put(tty); } rtnl_unlock(); } @@ -355,8 +358,6 @@ static void ldisc_close(struct tty_struct *tty) { struct ser_device *ser = tty->disc_data; - tty_kref_put(ser->tty); - spin_lock(&ser_lock); list_move(&ser->node, &ser_release_list); spin_unlock(&ser_lock); -- 2.51.0