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UBSAN: shift-out-of-bounds in exfat_fill_super

Status: upstream: reported C repro on 2025/05/30 13:08
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+967aa521d54edf6fb900@syzkaller.appspotmail.com
First crash: 106d, last: 4d19h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/05/30 lts (merge base) 98f47d0e9b8c C [report] UBSAN: shift-out-of-bounds in exfat_fill_super
2025/05/30 upstream (ToT) 8477ab143069 C Didn't crash
▶ ▼ Similar bugs (4)
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 669d 665d 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 C error 3 1674d 1691d 20/29 fixed on 2021/04/09 19:46
linux-5.15 UBSAN: shift-out-of-bounds in exfat_fill_super -1 1 92d 92d 0/3 upstream: reported on 2025/06/13 09:33
android-6-1 UBSAN: shift-out-of-bounds in exfat_fill_super origin:upstream -1 C 3 23d 150d 0/2 upstream: reported C repro on 2025/04/16 14:18
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2025/06/14 10:36 6m retest repro android13-5.15-lts report log
2025/06/14 10:36 11m retest repro android13-5.15-lts report log
2025/06/14 10:36 6m retest repro android13-5.15-lts report log
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2025/08/14 22:50 1h31m bisect fix android13-5.15-lts OK (0) job log log
2025/07/15 17:50 1h13m bisect fix android13-5.15-lts OK (0) job log log

Sample crash report:
exFAT-fs (loop2): Volume was not properly unmounted. Some data may be corrupt. Please run fsck.
exFAT-fs (loop2): Medium has reported failures. Some data may be lost.
================================================================================
UBSAN: shift-out-of-bounds in fs/exfat/super.c:520:38
shift exponent 200 is too large for 32-bit type 'int'
CPU: 0 PID: 378 Comm: syz.2.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 dump_stack+0x15/0x20 lib/dump_stack.c:113
 ubsan_epilogue+0xe/0x40 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+0x2930/0x2d00 fs/exfat/super.c:644
 get_tree_bdev+0x433/0x670 fs/super.c:1325
 exfat_get_tree+0x1c/0x20 fs/exfat/super.c:716
 vfs_get_tree+0x89/0x260 fs/super.c:1530
 do_new_mount+0x25a/0xa20 fs/namespace.c:3025
 path_mount+0x675/0x1020 fs/namespace.c:3355
 do_mount fs/namespace.c:3368 [inline]
 __do_sys_mount fs/namespace.c:3576 [inline]
 __se_sys_mount+0x318/0x380 fs/namespace.c:3553
 __x64_sys_mount+0xbf/0xd0 fs/namespace.c:3553
 x64_sys_call+0x6bf/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:166
 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: 0033:0x7f698aeb438a
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:00007f698ad22e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f698ad22ef0 RCX: 00007f698aeb438a
RDX: 00002000000005c0 RSI: 0000200000000240 RDI: 00007f698ad22eb0
RBP: 00002000000005c0 R08: 00007f698ad22ef0 R09: 0000000003800052
R10: 0000000003800052 R11: 0000000000000246 R12: 0000200000000240
R13: 00007f698ad22eb0 R14: 00000000000014fe R15: 0000200000000600
 </TASK>
================================================================================
exFAT-fs (loop2): logical sector size too small for device (logical sector size = 256)
exFAT-fs (loop2): failed to read boot sector
exFAT-fs (loop2): failed to recognize exfat type

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/09/08 21:46 android13-5.15-lts 1cd26e1d9a89 d291dd2d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro #1 (corrupt fs)] [mounted in repro #2 (corrupt fs)] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/05/30 14:09 android13-5.15-lts 4032a894ccb2 3d2f584d .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/05/30 13:36 android13-5.15-lts 4032a894ccb2 3d2f584d .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/05/30 13:02 android13-5.15-lts 4032a894ccb2 3d2f584d .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/09/08 20:55 android13-5.15-lts 1cd26e1d9a89 d291dd2d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/05/30 12:22 android13-5.15-lts 4032a894ccb2 3d2f584d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
* Struck through repros no longer work on HEAD.