KMSAN: uninit-value in caif_seqpkt_sendmsg

[syzbot]

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+09a5d5...@syzkaller.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@__sys_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
=====================================================


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[Eric Dumazet]

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;