general protection fault in p9_fd_create_unix

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 092150a25cb7 Merge branch 'for-linus' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15f31a2c400000
kernel config: https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
dashboard link: https://syzkaller.appspot.com/bug?extid=1a262da37d3bead15c39
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
userspace arch: i386
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=17492cc2400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=145aec58400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1a262d...@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
CPU: 1 PID: 4527 Comm: syz-executor611 Not tainted 4.18.0-rc4+ #42
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:strlen+0x1f/0xa0 lib/string.c:479
Code: ff ff ff 0f 1f 84 00 00 00 00 00 48 b8 00 00 00 00 00 fc ff df 55 48
89 fa 48 c1 ea 03 48 89 e5 41 54 49 89 fc 53 48 83 ec 08 <0f> b6 04 02 48
89 fa 83 e2 07 38 d0 7f 04 84 c0 75 4d 41 80 3c 24
RSP: 0018:ffff8801ad1d7398 EFLAGS: 00010292
RAX: dffffc0000000000 RBX: 1ffff10035a3ae7b RCX: ffffffff8766d02b
RDX: 0000000000000000 RSI: ffffffff87679de2 RDI: 0000000000000000
RBP: ffff8801ad1d73b0 R08: ffff8801d9762200 R09: 0000000000000000
R10: ffffed003b5e46d6 R11: ffff8801daf236b3 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff10035a3aeb2
FS: 0000000000000000(0000) GS:ffff8801daf00000(0063) knlGS:0000000009aa8840
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000200003c0 CR3: 00000001d96e0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
strlen include/linux/string.h:267 [inline]
p9_fd_create_unix+0xbf/0x370 net/9p/trans_fd.c:993
p9_client_create+0x915/0x16c9 net/9p/client.c:1062
v9fs_session_init+0x21a/0x1a80 fs/9p/v9fs.c:400
v9fs_mount+0x7c/0x900 fs/9p/vfs_super.c:135
mount_fs+0xae/0x328 fs/super.c:1277
vfs_kern_mount.part.34+0xdc/0x4e0 fs/namespace.c:1037
vfs_kern_mount fs/namespace.c:1027 [inline]
do_new_mount fs/namespace.c:2518 [inline]
do_mount+0x581/0x30e0 fs/namespace.c:2848
__do_compat_sys_mount fs/compat.c:125 [inline]
__se_compat_sys_mount fs/compat.c:92 [inline]
__ia32_compat_sys_mount+0x5d5/0x860 fs/compat.c:92
do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
do_fast_syscall_32+0x34d/0xfb2 arch/x86/entry/common.c:397
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f09cb9
Code: 55 08 8b 88 64 cd ff ff 8b 98 68 cd ff ff 89 c8 85 d2 74 02 89 0a 5b
5d c3 8b 04 24 c3 8b 1c 24 c3 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:00000000ff943bac EFLAGS: 00000286 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000200000c0
RDX: 0000000020000340 RSI: 0000000000000000 RDI: 00000000200006c0
RBP: 0000000000000008 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
Dumping ftrace buffer:
(ftrace buffer empty)
---[ end trace fe903ba4024485fe ]---
RIP: 0010:strlen+0x1f/0xa0 lib/string.c:479
Code: ff ff ff 0f 1f 84 00 00 00 00 00 48 b8 00 00 00 00 00 fc ff df 55 48
89 fa 48 c1 ea 03 48 89 e5 41 54 49 89 fc 53 48 83 ec 08 <0f> b6 04 02 48
89 fa 83 e2 07 38 d0 7f 04 84 c0 75 4d 41 80 3c 24
RSP: 0018:ffff8801ad1d7398 EFLAGS: 00010292
RAX: dffffc0000000000 RBX: 1ffff10035a3ae7b RCX: ffffffff8766d02b
RDX: 0000000000000000 RSI: ffffffff87679de2 RDI: 0000000000000000
RBP: ffff8801ad1d73b0 R08: ffff8801d9762200 R09: 0000000000000000
R10: ffffed003b5e46d6 R11: ffff8801daf236b3 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff10035a3aeb2
FS: 0000000000000000(0000) GS:ffff8801daf00000(0063) knlGS:0000000009aa8840
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000200003c0 CR3: 00000001d96e0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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