[v6.6] UBSAN: shift-out-of-bounds in befs_check_sb

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5fa4793a2d2d Linux 6.6.119
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=11076984580000
kernel config: https://syzkaller.appspot.com/x/.config?x=691a6769a86ac817
dashboard link: https://syzkaller.appspot.com/bug?extid=f3b996ee2b7d1ffea6bc
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/63699875f1dd/disk-5fa4793a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8506652fcb6f/vmlinux-5fa4793a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1b30ceed1710/bzImage-5fa4793a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f3b996...@syzkaller.appspotmail.com

loop7: detected capacity change from 0 to 128
================================================================================
UBSAN: shift-out-of-bounds in fs/befs/super.c:96:9
shift exponent 2066842816 is too large for 32-bit type 'int'
CPU: 1 PID: 9209 Comm: syz.7.753 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:217
__ubsan_handle_shift_out_of_bounds+0x380/0x400 lib/ubsan.c:387
befs_check_sb+0x419/0x4c0 fs/befs/super.c:96
befs_fill_super+0x8b2/0xe50 fs/befs/linuxvfs.c:873
mount_bdev+0x22b/0x2d0 fs/super.c:1643
legacy_get_tree+0xea/0x180 fs/fs_context.c:662
vfs_get_tree+0x8c/0x280 fs/super.c:1764
do_new_mount+0x24b/0xa40 fs/namespace.c:3386
do_mount fs/namespace.c:3726 [inline]
__do_sys_mount fs/namespace.c:3935 [inline]
__se_sys_mount+0x2da/0x3c0 fs/namespace.c:3912
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7ff50cf90eea
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff50ddfde68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ff50ddfdef0 RCX: 00007ff50cf90eea
RDX: 0000200000000040 RSI: 0000200000000000 RDI: 00007ff50ddfdeb0
RBP: 0000200000000040 R08: 00007ff50ddfdef0 R09: 0000000000800001
R10: 0000000000800001 R11: 0000000000000246 R12: 0000200000000000
R13: 00007ff50ddfdeb0 R14: 0000000000009e17 R15: 0000200000000080
</TASK>
================================================================================


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 5fa4793a2d2d Linux 6.6.119
git tree: linux-6.6.y

console output: https://syzkaller.appspot.com/x/log.txt?x=11766392580000

kernel config: https://syzkaller.appspot.com/x/.config?x=691a6769a86ac817
dashboard link: https://syzkaller.appspot.com/bug?extid=f3b996ee2b7d1ffea6bc
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=122bd77c580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1475b31a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/63699875f1dd/disk-5fa4793a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8506652fcb6f/vmlinux-5fa4793a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1b30ceed1710/bzImage-5fa4793a.xz

mounted in repro: https://storage.googleapis.com/syzbot-assets/17f230bdee43/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f3b996...@syzkaller.appspotmail.com

syz.0.17[5926]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
loop0: detected capacity change from 0 to 128

================================================================================
UBSAN: shift-out-of-bounds in fs/befs/super.c:96:9
shift exponent 2066842816 is too large for 32-bit type 'int'

CPU: 0 PID: 5926 Comm: syz.0.17 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:217
__ubsan_handle_shift_out_of_bounds+0x380/0x400 lib/ubsan.c:387
befs_check_sb+0x419/0x4c0 fs/befs/super.c:96
befs_fill_super+0x8b2/0xe50 fs/befs/linuxvfs.c:873
mount_bdev+0x22b/0x2d0 fs/super.c:1643
legacy_get_tree+0xea/0x180 fs/fs_context.c:662
vfs_get_tree+0x8c/0x280 fs/super.c:1764
do_new_mount+0x24b/0xa40 fs/namespace.c:3386
do_mount fs/namespace.c:3726 [inline]
__do_sys_mount fs/namespace.c:3935 [inline]
__se_sys_mount+0x2da/0x3c0 fs/namespace.c:3912
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

RIP: 0033:0x7f81beb90eea

Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 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 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007fff98e98d18 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007fff98e98da0 RCX: 00007f81beb90eea
RDX: 0000200000000040 RSI: 0000200000000000 RDI: 00007fff98e98d60
RBP: 0000200000000040 R08: 00007fff98e98da0 R09: 0000000000800001

R10: 0000000000800001 R11: 0000000000000246 R12: 0000200000000000

R13: 00007fff98e98d60 R14: 0000000000009e17 R15: 0000200000000080
</TASK>
================================================================================


---
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