From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 1F3F8427F85; Fri, 4 Sep 2026 06:19:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788502800; cv=none; b=KO4twPN04OqCYliybePLebEuoPnBY5LE46MlUA6uIbp0b87q3BGgbyLzgugO7jHPS83yqyIZdL38e2KqiaJEEq376owAuLUY9O920VfqkQ9dpFFThZ/q8FJ4Kqo4LZkmIC1vrLWy65Ts4Ld17wYJK0APMJNFEd6hlTZiLJeRzME= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788502800; c=relaxed/simple; bh=Ny2kpst0phxWGDMfetjZ04rjN6b6MFapL/USkLnWmzI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ptte0cAXECmpQ3WBWWJy/+av3FkxOkjvLKFlYrmGzrMgmb8VGVrohDQv8XmP3qqJVy40DfIfRmt7fy0BxToG811+St/JBpPc/jO3ABPk6eWd9kTS78ieNohBdoVPEUUpbtz+LL25oZ9XzG9tVB1UdzKT25C7va/PoO3W9dghmMs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=US7TspH2; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="US7TspH2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 79E6B1F00A3D; Fri, 4 Sep 2026 06:19:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788502799; bh=siHzXB4HY7ikPqAh7cf8Y82bCpCVC1AbCskBddauGms=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=US7TspH2XGWUATjs0IaCNpByt09LFcCFdrR5pdHmZQZtY3KT4O6ble8uHLTFy6ugF xeKKNmjMzQeMNAs2awYIsog+b0p9kZIam9uD1XIbExhZEXoKmdjt0qahzwSgJTQXM5 RS86TOhmLrF4bf2tqkDENOCINvTLIgI63k9ulcts= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jakub Kicinski , Aleksandr Khromov , Paolo Abeni Subject: [PATCH 6.12 335/403] slip: fix use-after-free in sl_sync() Date: Fri, 4 Sep 2026 07:02:18 +0200 Message-ID: <20260904045742.440431920@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260904045734.806166532@linuxfoundation.org> References: <20260904045734.806166532@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aleksandr Khromov commit 2c4e7c42d77e78ad595dbb9e4b5886b58b45d89d upstream. slip_devs[] stores bare net_device pointers and takes no reference on them. sl_sync() and sl_alloc() walk that table from slip_open() under rtnl_lock(), while an entry is dropped by sl_free_netdev(), which sl_setup() installs as dev->priv_destructor. priv_destructor is called from netdev_run_todo(), which deliberately runs with the RTNL semaphore released so that it can sleep while waiting for the device refcount to drop: /* Snapshot list, allow later requests */ list_replace_init(&net_todo_list, &list); __rtnl_unlock(); ... if (dev->priv_destructor) dev->priv_destructor(dev); /* slip_devs[i] = NULL */ if (dev->needs_free_netdev) free_netdev(dev); ... /* Free network device */ kobject_put(&dev->dev.kobj); So rtnl_lock() does not serialise slip_open() against the teardown at all. sl_sync() can load slip_devs[i] while the entry is still published and dereference it after netdev_run_todo() has run the destructor and released the device: CPU0 (slip_open) CPU1 (slip_close) unregister_netdev() rtnl_unlock() netdev_run_todo() __rtnl_unlock() rtnl_lock() sl_sync() dev = slip_devs[i] priv_destructor(dev) slip_devs[i] = NULL kobject_put(&dev->dev.kobj) /* dev is freed */ sl = netdev_priv(dev) if (sl->tty || sl->leased) /* use-after-free */ BUG: KASAN: use-after-free in sl_sync drivers/net/slip/slip.c:730 [inline] BUG: KASAN: use-after-free in slip_open+0xef4/0x1210 drivers/net/slip/slip.c:806 Read of size 1 at addr ffff8880712dac71 by task syz-executor.2/6506 CPU: 2 PID: 6506 Comm: syz-executor.2 Not tainted 6.1.134-syzkaller-00260-g0c8fc3469765 #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 Call Trace: sl_sync drivers/net/slip/slip.c:730 [inline] slip_open+0xef4/0x1210 drivers/net/slip/slip.c:806 tty_ldisc_open+0xa2/0x120 drivers/tty/tty_ldisc.c:433 tty_set_ldisc+0x324/0x720 drivers/tty/tty_ldisc.c:564 tiocsetd drivers/tty/tty_io.c:2428 [inline] tty_ioctl+0x5f0/0x1530 drivers/tty/tty_io.c:2712 Allocated by task 6502: alloc_netdev_mqs+0x98/0xfe0 net/core/dev.c:10719 sl_alloc drivers/net/slip/slip.c:756 [inline] slip_open+0x36d/0x1210 drivers/net/slip/slip.c:817 tty_ldisc_open+0xa2/0x120 drivers/tty/tty_ldisc.c:433 tty_set_ldisc+0x324/0x720 drivers/tty/tty_ldisc.c:564 Freed by task 6497: device_release+0xa2/0x240 drivers/base/core.c:2507 kobject_put+0x179/0x280 lib/kobject.c:729 netdev_run_todo+0x6c8/0xef0 net/core/dev.c:10509 slip_close+0x166/0x1c0 drivers/net/slip/slip.c:906 tty_ldisc_close+0x113/0x1a0 drivers/tty/tty_ldisc.c:456 tty_ldisc_kill+0x94/0x160 drivers/tty/tty_ldisc.c:614 tty_ldisc_release+0xe3/0x2b0 drivers/tty/tty_ldisc.c:782 tty_release+0xbcc/0xe70 drivers/tty/tty_io.c:1860 Commit e58c19124189 ("slip: Fix use-after-free Read in slip_open") fixed a different source of stale entries - a device left in slip_devs[] after slip_open() freed it on the registration error path - and does not address this race, which is why the report survives it. Drop the entry from ndo_uninit instead. unregister_netdevice() calls ndo_uninit under RTNL, before the device is queued to netdev_run_todo(), so an entry that sl_sync() can still see while holding RTNL belongs to a device that cannot be freed until RTNL is dropped. sl_free_netdev() stays only for the slip_open() error path, where register_netdevice() may have failed before ndo_init and ndo_uninit is then not called either. Both running for the same device is harmless: they run under the same RTNL section, so the slot cannot have been reused in between. This also removes the second symptom of the missing exclusion: a destructor running after sl_alloc() had already handed the slot out to another channel used to clear a live entry, so sl_sync() stopped at that NULL, sl_alloc() returned the same index again, and register_netdevice() failed with -EEXIST because slN was still there. Reproduced on x86_64 with several threads looping over open("/dev/ptmx") + ioctl(TIOCSETD, N_SLIP) + close(). Found by Linux Verification Center (linuxtesting.org) with Syzkaller. Fixes: 5342b77c4123 ("slip: Clean up create and destroy") Cc: stable@vger.kernel.org Suggested-by: Jakub Kicinski Signed-off-by: Aleksandr Khromov Link: https://patch.msgid.link/20260824100547.164773-1-haa@amicon.ru Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman --- drivers/net/slip/slip.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) --- a/drivers/net/slip/slip.c +++ b/drivers/net/slip/slip.c @@ -628,9 +628,15 @@ static void sl_uninit(struct net_device struct slip *sl = netdev_priv(dev); sl_free_bufs(sl); + /* Drop the slip_devs[] entry here rather than from the destructor: + * ndo_uninit runs under RTNL, so it cannot race sl_sync(). + */ + slip_devs[dev->base_addr] = NULL; } -/* Hook the destructor so we can free slip devices at the right point in time */ +/* Only for the slip_open() error path: register_netdevice() can fail before + * ndo_init, and then ndo_uninit is not called either. + */ static void sl_free_netdev(struct net_device *dev) { int i = dev->base_addr; @@ -657,7 +663,6 @@ static void sl_setup(struct net_device * { dev->netdev_ops = &sl_netdev_ops; dev->needs_free_netdev = true; - dev->priv_destructor = sl_free_netdev; dev->hard_header_len = 0; dev->addr_len = 0; @@ -908,7 +913,7 @@ static void slip_close(struct tty_struct #endif /* Flush network side */ unregister_netdev(sl->dev); - /* This will complete via sl_free_netdev */ + /* sl_uninit() has dropped the slip_devs[] entry by now */ } static void slip_hangup(struct tty_struct *tty)