[syzbot] [v9fs?] UBSAN: shift-out-of-bounds in v9fs_get_tree

[syzbot <syzbot+30c83da54e948f6e9436@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    3ac864c2d9bb Add linux-next specific files for 20250818
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=13706442580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6d1acc6b9e1fca1b
dashboard link: https://syzkaller.appspot.com/bug?extid=30c83da54e948f6e9436
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=141586f0580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=124c9ba2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/37dbe82593f0/disk-3ac864c2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d2fea0824445/vmlinux-3ac864c2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6f2a83735a01/bzImage-3ac864c2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+30c83da54e948f6e9436@syzkaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in fs/9p/vfs_super.c:57:22
shift exponent 32 is too large for 32-bit type 'int'
CPU: 0 UID: 0 PID: 5861 Comm: syz-executor379 Not tainted 6.17.0-rc2-next-20250818-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x40 lib/ubsan.c:233
 __ubsan_handle_shift_out_of_bounds+0x386/0x410 lib/ubsan.c:494
 v9fs_fill_super fs/9p/vfs_super.c:57 [inline]
 v9fs_get_tree+0x957/0xa90 fs/9p/vfs_super.c:125
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1752
 do_new_mount+0x2a2/0xa30 fs/namespace.c:3810
 do_mount fs/namespace.c:4138 [inline]
 __do_sys_mount fs/namespace.c:4349 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4326
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff35edd46a9
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeee8a4078 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00002000000025c0 RCX: 00007ff35edd46a9
RDX: 00002000000000c0 RSI: 00002000000025c0 RDI: 0000000000000000
RBP: 0000200000000280 R08: 0000200000000280 R09: 00007ffeee8a4258
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff35ee1d017
R13: 00007ffeee8a4248 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
---[ end trace ]---


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