UBSAN: shift-out-of-bounds in exfat_fill_super (2)

Status: upstream: reported C repro on 2025/09/21 18:12
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+84d69a20f88fd2cc8e89@syzkaller.appspotmail.com
First crash: 324d, last: 19d
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: UBSAN: shift-out-of-bounds in exfat_fill_super (log)
Repro: C syz .config
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/09/27 linux-5.15.y (ToT) 43bb85222e53 C [report] UBSAN: shift-out-of-bounds in exfat_fill_super
2025/09/27 upstream (ToT) fec734e8d564 C Didn't crash
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream UBSAN: shift-out-of-bounds in exfat_fill_super (2) exfat -1 1 1002d 998d 0/29 auto-obsoleted due to no activity on 2024/02/22 05:01
upstream UBSAN: shift-out-of-bounds in exfat_fill_super exfat -1 syz, C error 3 2007d 2024d 20/29 fixed on 2021/04/09 19:46
linux-5.15 UBSAN: shift-out-of-bounds in exfat_fill_super -1 1 425d 425d 0/3 auto-obsoleted due to no activity on 2025/09/21 09:33
android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super origin:lts -1 syz, C 21 14d 439d 0/2 upstream: reported C repro on 2025/05/30 13:08
android-6-1 UBSAN: shift-out-of-bounds in exfat_fill_super origin:upstream -1 syz, C error 15 21d 483d 0/2 upstream: reported C repro on 2025/04/16 14:18
▶ ▼ Last patch testing requests (7)
Created Duration User Patch Repo Result
2026/07/24 16:56 15m retest repro linux-5.15.y report log
2026/05/28 00:59 16m retest repro linux-5.15.y report log
2026/05/11 18:20 25m retest repro linux-5.15.y report log
2026/03/13 02:07 6m retest repro linux-5.15.y error
2026/02/26 22:06 10m retest repro linux-5.15.y report log
2026/01/01 23:52 10m retest repro linux-5.15.y report log
2025/10/11 05:27 15m retest repro linux-5.15.y report log
▶ ▼ Fix bisection attempts (7)
Created Duration User Patch Repo Result
2026/07/10 13:32 12h22m fix candidate upstream error job log
2026/06/07 00:14 12m fix candidate upstream error job log
2026/03/25 22:19 9m fix candidate upstream error job log
2026/02/22 23:48 1m fix candidate upstream error job log
2026/01/23 06:36 1m fix candidate upstream error job log
2025/12/18 19:27 2h00m bisect fix linux-5.15.y OK (0) job log log
2025/11/15 12:55 2h22m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
exFAT-fs (loop0): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
exFAT-fs (loop0): Medium has reported failures. Some data may be lost.
================================================================================
UBSAN: shift-out-of-bounds in fs/exfat/super.c:520:38
shift exponent 116 is too large for 32-bit type 'int'
CPU: 1 PID: 4347 Comm: syz.0.24 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 ubsan_epilogue+0xa/0x30 lib/ubsan.c:151
 __ubsan_handle_shift_out_of_bounds+0x37c/0x400 lib/ubsan.c:321
 exfat_read_boot_sector fs/exfat/super.c:520 [inline]
 __exfat_fill_super fs/exfat/super.c:576 [inline]
 exfat_fill_super+0x2943/0x2cf0 fs/exfat/super.c:644
 get_tree_bdev+0x3f1/0x610 fs/super.c:1325
 vfs_get_tree+0x88/0x270 fs/super.c:1530
 do_new_mount+0x24a/0xa40 fs/namespace.c:3025
 do_mount fs/namespace.c:3368 [inline]
 __do_sys_mount fs/namespace.c:3576 [inline]
 __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3553
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f85a7b223ca
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:00007f85a718fe68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f85a718fef0 RCX: 00007f85a7b223ca
RDX: 00002000000005c0 RSI: 0000200000000240 RDI: 00007f85a718feb0
RBP: 00002000000005c0 R08: 00007f85a718fef0 R09: 0000000003800052
R10: 0000000003800052 R11: 0000000000000246 R12: 0000200000000240
R13: 00007f85a718feb0 R14: 00000000000014fe R15: 0000200000000600
 </TASK>
================================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/09/21 20:27 linux-5.15.y 43bb85222e53 67c37560 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-5-15-kasan UBSAN: shift-out-of-bounds in exfat_fill_super
2025/09/21 19:39 linux-5.15.y 43bb85222e53 67c37560 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-5-15-kasan UBSAN: shift-out-of-bounds in exfat_fill_super
2025/09/21 18:11 linux-5.15.y 43bb85222e53 67c37560 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan UBSAN: shift-out-of-bounds in exfat_fill_super
* Struck through repros no longer work on HEAD.