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Date:   Tue, 19 May 2020 18:24:43 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        syzbot <syzkaller@...glegroups.com>
Subject: [PATCH net] ax24: fix setsockopt(SO_BINDTODEVICE)

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@...5_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@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
---
 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 ff57ea89c27e652c1128f68e69e22d41be361dac..fd91cd34f25e03d0178cbe66568ed392a7013f4e 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;
-- 
2.26.2.761.g0e0b3e54be-goog

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