[PATCH 3.16 05/61] slip: Fix use-after-free Read in slip_open

From: Ben Hutchings <ben@decadent.org.uk>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: akpm@linux-foundation.org, Denis Kirjanov <kda@linux-powerpc.org>,
	"Jouni Hogander" <jouni.hogander@unikie.com>,
	"Lukas Bulwahn" <lukas.bulwahn@gmail.com>,
	"David Miller" <davem@davemloft.net>,
	"Oliver Hartkopp" <socketcan@hartkopp.net>,
	syzbot+4d5170758f3762109542@syzkaller.appspotmail.com
Subject: [PATCH 3.16 05/61] slip: Fix use-after-free Read in slip_open
Date: Tue, 09 Jun 2020 19:03:56 +0100	[thread overview]
Message-ID: <lsq.1591725832.69289718@decadent.org.uk> (raw)
In-Reply-To: <lsq.1591725831.850867383@decadent.org.uk>

3.16.85-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jouni Hogander <jouni.hogander@unikie.com>

commit e58c1912418980f57ba2060017583067f5f71e52 upstream.

Slip_open doesn't clean-up device which registration failed from the
slip_devs device list. On next open after failure this list is iterated
and freed device is accessed. Fix this by calling sl_free_netdev in error
path.

Here is the trace from the Syzbot:

__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:634
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132
sl_sync drivers/net/slip/slip.c:725 [inline]
slip_open+0xecd/0x11b7 drivers/net/slip/slip.c:801
tty_ldisc_open.isra.0+0xa3/0x110 drivers/tty/tty_ldisc.c:469
tty_set_ldisc+0x30e/0x6b0 drivers/tty/tty_ldisc.c:596
tiocsetd drivers/tty/tty_io.c:2334 [inline]
tty_ioctl+0xe8d/0x14f0 drivers/tty/tty_io.c:2594
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: 3b5a39979daf ("slip: Fix memory leak in slip_open error path")
Reported-by: syzbot+4d5170758f3762109542@syzkaller.appspotmail.com
Cc: David Miller <davem@davemloft.net>
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jouni Hogander <jouni.hogander@unikie.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: sl_free_netdev() calls free_netdev() here, so
 delete the direct call to free_netdev()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

--- a/drivers/net/slip/slip.c
+++ b/drivers/net/slip/slip.c
@@ -867,7 +867,7 @@ err_free_chan:
 	sl->tty = NULL;
 	tty->disc_data = NULL;
 	clear_bit(SLF_INUSE, &sl->flags);
-	free_netdev(sl->dev);
+	sl_free_netdev(sl->dev);
 
 err_exit:
 	rtnl_unlock();

