linux-kernel - Forwarded: Re: [syzbot] [v9fs?] UBSAN: shift-out-of-bounds in v9fs_get

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Message-ID: <68d8b2d7.050a0220.25d7ab.046b.GAE@google.com>
Date: Sat, 27 Sep 2025 21:00:23 -0700
From: syzbot <syzbot+30c83da54e948f6e9436@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Forwarded: Re: [syzbot] [v9fs?] UBSAN: shift-out-of-bounds in v9fs_get_tree

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***

Subject: Re: [syzbot] [v9fs?] UBSAN: shift-out-of-bounds in v9fs_get_tree
Author: xandfury@...il.com

syzbot <syzbot+30c83da54e948f6e9436@...kaller.appspotmail.com> writes:

> 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@...kaller.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 ]—
>
>
> —
> This report 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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> <https://goo.gl/tpsmEJ#status> for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
>
> If you want to overwrite report’s subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master