netdev - [PATCH] slip: Fix use-after-free Read in slip

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Message-Id: <20191125122343.17904-1-jouni.hogander@unikie.com>
Date:   Mon, 25 Nov 2019 14:23:43 +0200
From:   jouni.hogander@...kie.com
To:     netdev@...r.kernel.org
Cc:     Jouni Hogander <jouni.hogander@...kie.com>,
        David Miller <davem@...emloft.net>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: [PATCH] slip: Fix use-after-free Read in slip_open

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

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@...kaller.appspotmail.com
Cc: David Miller <davem@...emloft.net>
Cc: Oliver Hartkopp <socketcan@...tkopp.net>
Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
Signed-off-by: Jouni Hogander <jouni.hogander@...kie.com>
---
 drivers/net/slip/slip.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/slip/slip.c b/drivers/net/slip/slip.c
index 4d479e3c817d..2a91c192659f 100644
--- a/drivers/net/slip/slip.c
+++ b/drivers/net/slip/slip.c
@@ -855,6 +855,7 @@ static int slip_open(struct tty_struct *tty)
 	sl->tty = NULL;
 	tty->disc_data = NULL;
 	clear_bit(SLF_INUSE, &sl->flags);
+	sl_free_netdev(sl->dev);
 	free_netdev(sl->dev);
 
 err_exit:
-- 
2.17.1