[syzbot] [fs?] UBSAN: shift-out-of-bounds in befs_check_sb

[syzbot]

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+fc26c3...@syzkaller.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>
================================================================================


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[syzbot]

syzbot suspects this issue was fixed by commit:

commit 6f861765464f43a71462d52026fbddfc858239a5
Author: Jan Kara <ja...@suse.cz>
Date: Wed Nov 1 17:43:10 2023 +0000

fs: Block writes to mounted block devices

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14b5e754180000
start commit: 8689f4f2ea56 Merge tag 'mmc-v6.5-2' of git://git.kernel.or..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=15873d91ff37a949
dashboard link: https://syzkaller.appspot.com/bug?extid=fc26c366038b54261e53
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14237dc2a80000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13e34d22a80000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: fs: Block writes to mounted block devices

For information about bisection process see: https://goo.gl/tpsmEJ#bisection