[PATCH 3.16 108/366] ip_tunnel: better validate user provided tunnel names

Ben Hutchings
2018-10-14T23:28:53Z

From: Eric Dumazet <edumazet@google.com>

commit 9cb726a212a82c88c98aa9f0037fd04777cd8fe5 upstream.

Use dev_valid_name() to make sure user does not provide illegal
device name.

syzbot caught the following bug :

BUG: KASAN: stack-out-of-bounds in strlcpy include/linux/string.h:300 [inline]
BUG: KASAN: stack-out-of-bounds in __ip_tunnel_create+0xca/0x6b0 net/ipv4/ip_tunnel.c:257
Write of size 20 at addr ffff8801ac79f810 by task syzkaller268107/4482

CPU: 0 PID: 4482 Comm: syzkaller268107 Not tainted 4.16.0+ #1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b9/0x29f lib/dump_stack.c:53
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0xac/0x2f5 mm/kasan/report.c:412
check_memory_region_inline mm/kasan/kasan.c:260 [inline]
check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
memcpy+0x37/0x50 mm/kasan/kasan.c:303
strlcpy include/linux/string.h:300 [inline]
__ip_tunnel_create+0xca/0x6b0 net/ipv4/ip_tunnel.c:257
ip_tunnel_create net/ipv4/ip_tunnel.c:352 [inline]
ip_tunnel_ioctl+0x818/0xd40 net/ipv4/ip_tunnel.c:861
ipip_tunnel_ioctl+0x1c5/0x420 net/ipv4/ipip.c:350
dev_ifsioc+0x43e/0xb90 net/core/dev_ioctl.c:334
dev_ioctl+0x69a/0xcc0 net/core/dev_ioctl.c:525
sock_ioctl+0x47e/0x680 net/socket.c:1015
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x1cf/0x1650 fs/ioctl.c:684
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
SYSC_ioctl fs/ioctl.c:708 [inline]
SyS_ioctl+0x24/0x30 fs/ioctl.c:706
do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7

Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/ipv4/ip_tunnel.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -300,13 +300,14 @@ static struct net_device *__ip_tunnel_cr
struct net_device *dev;
char name[IFNAMSIZ];

- if (parms->name[0])
+ err = -E2BIG;
+ if (parms->name[0]) {
+ if (!dev_valid_name(parms->name))
+ goto failed;
strlcpy(name, parms->name, IFNAMSIZ);
- else {
- if (strlen(ops->kind) > (IFNAMSIZ - 3)) {
- err = -E2BIG;
+ } else {
+ if (strlen(ops->kind) > (IFNAMSIZ - 3))
goto failed;
- }
strlcpy(name, ops->kind, IFNAMSIZ);
strncat(name, "%d", 2);
}