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From:   Kyungtae Kim <kt0755@gmail.com>
Date:   Thu, 24 Jan 2019 08:03:38 -0500
Message-ID: <CAEAjams=qBWe0V+mOW3V=34vWAKeqNvjNxr3fZdpC6fL6-32Fg@mail.gmail.com>
Subject: Re: UBSAN: Undefined behaviour in net/ipv4/ip_output.c
To:     Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Byoungyoung Lee <lifeasageek@gmail.com>,
        DaeRyong Jeong <threeearcat@gmail.com>,
        syzkaller <syzkaller@googlegroups.com>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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That's my bad. Thank you for your comment and effort.

Regards,
Kyungtae Kim


On Wed, Jan 23, 2019 at 4:34 PM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Mon, Jan 21, 2019 at 2:25 PM Kyungtae Kim <kt0755@gmail.com> 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