KMSAN: uninit-value in p9_client_rpc

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    b64f7ec04e12 kmsan: implement kmsan_memmove_shadow() and k..
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=127179b2400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=93d57043084eee38
dashboard link: https://syzkaller.appspot.com/bug?extid=4de40388f584432bf004
compiler:       clang version 7.0.0 (trunk 334104)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4de40388f584432bf004@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KMSAN: uninit-value in p9_client_rpc+0x194c/0x1dc0 net/9p/client.c:818
CPU: 0 PID: 14601 Comm: syz-executor4 Not tainted 4.18.0-rc4+ #24
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+0x185/0x1e0 lib/dump_stack.c:113
 kmsan_report+0x195/0x2c0 mm/kmsan/kmsan.c:1092
 __msan_warning_32+0x7d/0xe0 mm/kmsan/kmsan_instr.c:640
 p9_client_rpc+0x194c/0x1dc0 net/9p/client.c:818
 p9_client_attach+0x35b/0xc30 net/9p/client.c:1147
 v9fs_session_init+0x24b9/0x2970 fs/9p/v9fs.c:449
 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+0xd30/0x5310 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:290
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x455e29
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f2b81f7fc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f2b81f806d4 RCX: 0000000000455e29
RDX: 0000000020000080 RSI: 0000000020000000 RDI: 0000000000000000
RBP: 000000000072bea0 R08: 0000000020000380 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c05ca R14: 00000000004d0070 R15: 0000000000000000

Local variable description: ----ecode.i@p9_client_rpc
Variable was created at:
 p9_client_rpc+0x183/0x1dc0 net/9p/client.c:750
 p9_client_attach+0x35b/0xc30 net/9p/client.c:1147
==================================================================


---
This bug 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@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with  
syzbot.