KMSAN: uninit-value in unix_find_other

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    a00de5aa4da3 kmsan: delete some dead code
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=165aa6d0400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b3fd30f86ca205e8
dashboard link: https://syzkaller.appspot.com/bug?extid=75d51fe5bf4ebe988518
compiler:       clang version 7.0.0 (trunk 334104)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=128012c2400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1221462c400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+75d51fe5bf4ebe988518@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KMSAN: uninit-value in __unix_find_socket_byname  
net/unix/af_unix.c:280 [inline]
BUG: KMSAN: uninit-value in unix_find_socket_byname net/unix/af_unix.c:303  
[inline]
BUG: KMSAN: uninit-value in unix_find_other+0x315/0xc60  
net/unix/af_unix.c:932
CPU: 1 PID: 4574 Comm: syz-executor354 Not tainted 4.17.0+ #22
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+0x185/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:990
 __msan_warning_32+0x70/0xc0 mm/kmsan/kmsan_instr.c:640
 __unix_find_socket_byname net/unix/af_unix.c:280 [inline]
 unix_find_socket_byname net/unix/af_unix.c:303 [inline]
 unix_find_other+0x315/0xc60 net/unix/af_unix.c:932
 unix_stream_connect+0x84e/0x26b0 net/unix/af_unix.c:1241
 p9_fd_create_unix+0x36b/0x5f0 net/9p/trans_fd.c:1019
 p9_client_create+0x1333/0x20e0 net/9p/client.c:1065
 v9fs_session_init+0x313/0x2830 fs/9p/v9fs.c:405
 v9fs_mount+0x107/0x11b0 fs/9p/vfs_super.c:135
 mount_fs+0x29b/0x780 fs/super.c:1277
 vfs_kern_mount+0x222/0x990 fs/namespace.c:1037
 do_new_mount fs/namespace.c:2518 [inline]
 do_mount+0xca5/0x4ed0 fs/namespace.c:2848
 ksys_mount+0x32e/0x3d0 fs/namespace.c:3064
 __do_sys_mount fs/namespace.c:3078 [inline]
 __se_sys_mount fs/namespace.c:3075 [inline]
 __x64_sys_mount+0x157/0x1c0 fs/namespace.c:3075
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x4400d9
RSP: 002b:00007fff30dec578 EFLAGS: 00000217 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00000000004400d9
RDX: 00000000200000c0 RSI: 0000000020000040 RDI: 0000000020000000
RBP: 00000000006ca018 R08: 0000000020000100 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000401960
R13: 00000000004019f0 R14: 0000000000000000 R15: 0000000000000000

Local variable description: ----sun_server@p9_fd_create_unix
Variable was created at:
 p9_fd_create_unix+0x7a/0x5f0 net/9p/trans_fd.c:996
 p9_client_create+0x1333/0x20e0 net/9p/client.c:1065
==================================================================


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