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Date:   Mon, 3 Aug 2020 09:41:14 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     syzbot <syzbot+09a5d591c1f98cf5efcb@...kaller.appspotmail.com>,
        alexios.zavras@...el.com, allison@...utok.net, davem@...emloft.net,
        edumazet@...gle.com, glider@...gle.com, gregkh@...uxfoundation.org,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, swinslow@...il.com,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de
Subject: Re: KMSAN: uninit-value in caif_seqpkt_sendmsg



On 8/3/20 9:35 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    8bbbc5cf kmsan: don't compile memmove
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=11fbfe09e00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cd0e9a6b0e555cc3
> dashboard link: https://syzkaller.appspot.com/bug?extid=09a5d591c1f98cf5efcb
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=150ef74ee00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=170e2109e00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+09a5d591c1f98cf5efcb@...kaller.appspotmail.com
> 
> =====================================================
> BUG: KMSAN: uninit-value in caif_seqpkt_sendmsg+0x693/0xf60 net/caif/caif_socket.c:542
> CPU: 1 PID: 11244 Comm: syz-executor620 Not tainted 5.6.0-rc2-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:118
>  __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
>  caif_seqpkt_sendmsg+0x693/0xf60 net/caif/caif_socket.c:542
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg net/socket.c:672 [inline]
>  ____sys_sendmsg+0x12b6/0x1350 net/socket.c:2343
>  ___sys_sendmsg net/socket.c:2397 [inline]
>  __sys_sendmmsg+0x808/0xc90 net/socket.c:2480
>  __compat_sys_sendmmsg net/compat.c:656 [inline]
>  __do_compat_sys_sendmmsg net/compat.c:663 [inline]
>  __se_compat_sys_sendmmsg net/compat.c:660 [inline]
>  __ia32_compat_sys_sendmmsg+0x127/0x180 net/compat.c:660
>  do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
>  do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410
>  entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139
> RIP: 0023:0xf7f79d99
> 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:00000000ffbf4d6c EFLAGS: 00000292 ORIG_RAX: 0000000000000159
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020007600
> RDX: 0000000000000001 RSI: 0000000000000000 RDI: 00000000080bb508
> RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> 
> Local variable ----iovstack.i@...ys_sendmmsg created at:
>  ___sys_sendmsg net/socket.c:2388 [inline]
>  __sys_sendmmsg+0x6db/0xc90 net/socket.c:2480
>  ___sys_sendmsg net/socket.c:2388 [inline]
>  __sys_sendmmsg+0x6db/0xc90 net/socket.c:2480
> =====================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
> 

It is not clear why this code tests iov_base instead of len.

diff --git a/net/caif/caif_socket.c b/net/caif/caif_socket.c
index 3ad0a1df6712834a7f70b21a78173a02c7cba897..e4540023a9404d44089ff11b8b912fa23d8de69f 100644
--- a/net/caif/caif_socket.c
+++ b/net/caif/caif_socket.c
@@ -539,7 +539,7 @@ static int caif_seqpkt_sendmsg(struct socket *sock, struct msghdr *msg,
                goto err;
 
        ret = -EINVAL;
-       if (unlikely(msg->msg_iter.iov->iov_base == NULL))
+       if (unlikely(!len))
                goto err;
        noblock = msg->msg_flags & MSG_DONTWAIT;
 

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