[PATCH 4.14 05/34] l2tp: fix infoleak in l2tp_ip6_recvmsg()

Greg Kroah-Hartman
2019-03-18T09:35:55Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 163d1c3d6f17556ed3c340d3789ea93be95d6c28 ]

Back in 2013 Hannes took care of most of such leaks in commit
bceaa90240b6 ("inet: prevent leakage of uninitialized memory to user in recv syscalls")

But the bug in l2tp_ip6_recvmsg() has not been fixed.

syzbot report :

BUG: KMSAN: kernel-infoleak in _copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
CPU: 1 PID: 10996 Comm: syz-executor362 Not tainted 5.0.0+ #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x173/0x1d0 lib/dump_stack.c:113
kmsan_report+0x12e/0x2a0 mm/kmsan/kmsan.c:600
kmsan_internal_check_memory+0x9f4/0xb10 mm/kmsan/kmsan.c:694
kmsan_copy_to_user+0xab/0xc0 mm/kmsan/kmsan_hooks.c:601
_copy_to_user+0x16b/0x1f0 lib/usercopy.c:32
copy_to_user include/linux/uaccess.h:174 [inline]
move_addr_to_user+0x311/0x570 net/socket.c:227
___sys_recvmsg+0xb65/0x1310 net/socket.c:2283
do_recvmmsg+0x646/0x10c0 net/socket.c:2390
__sys_recvmmsg net/socket.c:2469 [inline]
__do_sys_recvmmsg net/socket.c:2492 [inline]
__se_sys_recvmmsg+0x1d1/0x350 net/socket.c:2485
__x64_sys_recvmmsg+0x62/0x80 net/socket.c:2485
do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x445819
Code: e8 6c b6 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 2b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f64453eddb8 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00000000006dac28 RCX: 0000000000445819
RDX: 0000000000000005 RSI: 0000000020002f80 RDI: 0000000000000003
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac2c
R13: 00007ffeba8f87af R14: 00007f64453ee9c0 R15: 20c49ba5e353f7cf

Local variable description: ----addr@___sys_recvmsg
Variable was created at:
___sys_recvmsg+0xf6/0x1310 net/socket.c:2244
do_recvmmsg+0x646/0x10c0 net/socket.c:2390

Bytes 0-31 of 32 are uninitialized
Memory access of size 32 starts at ffff8880ae62fbb0
Data copied to user address 0000000020000000

Fixes: a32e0eec7042 ("l2tp: introduce L2TPv3 IP encapsulation support for IPv6")
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/l2tp/l2tp_ip6.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -684,9 +684,6 @@ static int l2tp_ip6_recvmsg(struct sock
if (flags & MSG_OOB)
goto out;

- if (addr_len)
- *addr_len = sizeof(*lsa);
-
if (flags & MSG_ERRQUEUE)
return ipv6_recv_error(sk, msg, len, addr_len);

@@ -716,6 +713,7 @@ static int l2tp_ip6_recvmsg(struct sock
lsa->l2tp_conn_id = 0;
if (ipv6_addr_type(&lsa->l2tp_addr) & IPV6_ADDR_LINKLOCAL)
lsa->l2tp_scope_id = inet6_iif(skb);
+ *addr_len = sizeof(*lsa);
}

if (np->rxopt.all)