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

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Message-ID: <68d997db.050a0220.1696c6.0009.GAE@google.com>
Date: Sun, 28 Sep 2025 13:17:31 -0700
From: syzbot <syzbot+fc26c366038b54261e53@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Forwarded: Re: [syzbot] [fs?] UBSAN: shift-out-of-bounds in befs_check_sb

For archival purposes, forwarding an incoming command email to
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***

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

syzbot <syzbot+fc26c366038b54261e53@...kaller.appspotmail.com> writes:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    3f01e9fed845 Merge tag ’linux-watchdog-6.5-rc2’ of git://w..
> git tree:       upstream
> console+strace: <https://syzkaller.appspot.com/x/log.txt?x=1310fc5ca80000>
> kernel config:  <https://syzkaller.appspot.com/x/.config?x=e6c2f785de9e303f>
> dashboard link: <https://syzkaller.appspot.com/bug?extid=fc26c366038b54261e53>
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      <https://syzkaller.appspot.com/x/repro.syz?x=107f12e8a80000>
> C reproducer:   <https://syzkaller.appspot.com/x/repro.c?x=174014a2a80000>
>
> Downloadable assets:
> disk image: <https://storage.googleapis.com/syzbot-assets/896ca272ae74/disk-3f01e9fe.raw.xz>
> vmlinux: <https://storage.googleapis.com/syzbot-assets/deff7fbe3b2c/vmlinux-3f01e9fe.xz>
> kernel image: <https://storage.googleapis.com/syzbot-assets/ca3863031cc5/bzImage-3f01e9fe.xz>
> mounted in repro: <https://storage.googleapis.com/syzbot-assets/9c7c5305480d/mount_0.gz>
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+fc26c366038b54261e53@...kaller.appspotmail.com
>
> memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=5019 ’syz-executor590’
> loop0: detected capacity change from 0 to 128
> `=============================================================================='
> UBSAN: shift-out-of-bounds in fs/befs/super.c:96:9
> shift exponent 3229888891 is too large for 32-bit type ’int’
> CPU: 0 PID: 5019 Comm: syz-executor590 Not tainted 6.5.0-rc1-syzkaller-00006-g3f01e9fed845 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
>  ubsan_epilogue lib/ubsan.c:217 [inline]
>  __ubsan_handle_shift_out_of_bounds+0x221/0x5a0 lib/ubsan.c:387
>  befs_check_sb.cold+0x19/0x6f fs/befs/super.c:96
>  befs_fill_super+0x9b5/0x1110 fs/befs/linuxvfs.c:873
>  mount_bdev+0x315/0x3e0 fs/super.c:1391
>  legacy_get_tree+0x109/0x220 fs/fs_context.c:611
>  vfs_get_tree+0x8d/0x350 fs/super.c:1519
>  do_new_mount fs/namespace.c:3335 [inline]
>  path_mount+0x136e/0x1e70 fs/namespace.c:3662
>  do_mount fs/namespace.c:3675 [inline]
>  __do_sys_mount fs/namespace.c:3884 [inline]
>  __se_sys_mount fs/namespace.c:3861 [inline]
>  __x64_sys_mount+0x283/0x300 fs/namespace.c:3861
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7fe1b84908ba
> Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 5e 04 00 00 66 2e 0f 1f
> 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007ffd994dbc28 EFLAGS: 00000282 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007ffd994dbc30 RCX: 00007fe1b84908ba
> RDX: 0000000020000100 RSI: 0000000020009e40 RDI: 00007ffd994dbc30
> RBP: 0000000000000004 R08: 00007ffd994dbc70 R09: 0000000000009e1f
> R10: 0000000003008001 R11: 0000000000000282 R12: 00007ffd994dbc70
> R13: 0000000000000003 R14: 0000000000010000 R15: 0000000000000001
>  </TASK>
> `=============================================================================='
>
>
> —
> 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 bug is already fixed, 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 change bug’s subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the bug is a duplicate of another bug, 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