Re: UBSAN: Undefined behaviour in net/ipv4/ip_output.c

[Willem de Bruijn]

On Mon, Jan 21, 2019 at 2:25 PM Kyungtae Kim <kt0755@xxxxxxxxx> wrote:
>
> I'm reporting a bug in linux-5.0-rc2: "UBSAN: Undefined behaviour in
> net/ipv4/ip_output.c"
>
> kernel config: https://kt0755.github.io/etc/config-5.0-rc2
> repro: https://kt0755.github.io/etc/repro.b6a11.c

Thanks for the report.

That reproducer does not seem to exercise system call sendmsg. Did you
mean to share another? Perhaps one that users SO_SNDBUFFORCE or
sysctl_wmem_max.

When constructing a reproducer, I did easily trigger an UBSAN warning
when setting SO_SNDBUFFORCE to INT_MAX - 1, so I can imagine that this
one can trigger, as well. As long as sk_sndbuf can be set to any
integer value, we'll have to be careful with any such multiplication.

> Integer overflow happened in __ip_append_data() when 2 * sk->sk_sndbuf
> (at line 1004)
> is larger than the boundary of the destination (i.e., int).
> Some sanity check code right before it would help.
>
> =========================================
> UBSAN: Undefined behaviour in net/ipv4/ip_output.c:1004:11
> signed integer overflow:
> 1282607372 * 2 cannot be represented in type 'int'
> CPU: 0 PID: 8465 Comm: syz-executor4 Not tainted 5.0.0-rc2 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0xb1/0x118 lib/dump_stack.c:113
>  ubsan_epilogue+0x12/0x94 lib/ubsan.c:159
>  handle_overflow+0x1cf/0x21a lib/ubsan.c:190
>  __ubsan_handle_mul_overflow+0x2a/0x35 lib/ubsan.c:214
>  __ip_append_data+0x30ed/0x3350 net/ipv4/ip_output.c:1004
>  ip_append_data.part.18+0xf3/0x170 net/ipv4/ip_output.c:1220
>  ip_append_data+0x63/0x80 net/ipv4/ip_output.c:1209
>  raw_sendmsg+0xd99/0x2b60 net/ipv4/raw.c:670
>  inet_sendmsg+0xfc/0x620 net/ipv4/af_inet.c:798
>  sock_sendmsg_nosec net/socket.c:621 [inline]
>  sock_sendmsg+0xdd/0x130 net/socket.c:631
>  ___sys_sendmsg+0x7b3/0x950 net/socket.c:2116
>  __sys_sendmsg+0xfc/0x1d0 net/socket.c:2154
>  __do_sys_sendmsg net/socket.c:2163 [inline]
>  __se_sys_sendmsg net/socket.c:2161 [inline]
>  __x64_sys_sendmsg+0x83/0xc0 net/socket.c:2161
>  do_syscall_64+0xbe/0x4f0 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4497b9
> Code: e8 8c 9f 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 9b 6b fc ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f0d0100bc68 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f0d0100c6cc RCX: 00000000004497b9
> RDX: 0000000000000000 RSI: 0000000020000500 RDI: 0000000000000013
> RBP: 000000000071bea0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000089a0 R14: 00000000006f1a40 R15: 00007f0d0100c700
> =========================================
>
> Thanks,
> Kyungtae