[PATCH AUTOSEL 5.6 207/606] ax25: fix setsockopt(SO_BINDTODEVICE)

Sasha Levin
2020-06-09T00:10:25Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 687775cec056b38a4c8f3291e0dd7a9145f7b667 ]

syzbot was able to trigger this trace [1], probably by using
a zero optlen.

While we are at it, cap optlen to IFNAMSIZ - 1 instead of IFNAMSIZ.

[1]
BUG: KMSAN: uninit-value in strnlen+0xf9/0x170 lib/string.c:569
CPU: 0 PID: 8807 Comm: syz-executor483 Not tainted 5.7.0-rc4-syzkaller #0
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+0x1c9/0x220 lib/dump_stack.c:118
kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
__msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
strnlen+0xf9/0x170 lib/string.c:569
dev_name_hash net/core/dev.c:207 [inline]
netdev_name_node_lookup net/core/dev.c:277 [inline]
__dev_get_by_name+0x75/0x2b0 net/core/dev.c:778
ax25_setsockopt+0xfa3/0x1170 net/ax25/af_ax25.c:654
__compat_sys_setsockopt+0x4ed/0x910 net/compat.c:403
__do_compat_sys_setsockopt net/compat.c:413 [inline]
__se_compat_sys_setsockopt+0xdd/0x100 net/compat.c:410
__ia32_compat_sys_setsockopt+0x62/0x80 net/compat.c:410
do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
do_fast_syscall_32+0x3bf/0x6d0 arch/x86/entry/common.c:398
entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f57dd9
Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000ffae8c1c EFLAGS: 00000217 ORIG_RAX: 000000000000016e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000000101
RDX: 0000000000000019 RSI: 0000000020000000 RDI: 0000000000000004
RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Local variable ----devname@ax25_setsockopt created at:
ax25_setsockopt+0xe6/0x1170 net/ax25/af_ax25.c:536
ax25_setsockopt+0xe6/0x1170 net/ax25/af_ax25.c:536

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
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/ax25/af_ax25.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index ff57ea89c27e..fd91cd34f25e 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -635,8 +635,10 @@ static int ax25_setsockopt(struct socket *sock, int level, int optname,
break;

case SO_BINDTODEVICE:
- if (optlen > IFNAMSIZ)
- optlen = IFNAMSIZ;
+ if (optlen > IFNAMSIZ - 1)
+ optlen = IFNAMSIZ - 1;
+
+ memset(devname, 0, sizeof(devname));

if (copy_from_user(devname, optval, optlen)) {
res = -EFAULT;
--
2.25.1