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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: 293d, last: 12d
▶ ▼ 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 (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 857d 853d 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 1862d 1879d 20/29 fixed on 2021/04/09 19:46
linux-5.15 UBSAN: shift-out-of-bounds in exfat_fill_super (2) origin:lts-only -1 C error 3 21d 179d 0/3 upstream: reported C repro on 2025/09/21 18:12
linux-5.15 UBSAN: shift-out-of-bounds in exfat_fill_super -1 1 279d 279d 0/3 auto-obsoleted due to no activity on 2025/09/21 09:33
android-6-1 UBSAN: shift-out-of-bounds in exfat_fill_super origin:upstream -1 C 12 9d22h 337d 0/2 upstream: reported C repro on 2025/04/16 14:18
▶ ▼ Last patch testing requests (8)
Created Duration User Patch Repo Result
2026/02/17 21:21 18m retest repro android13-5.15-lts report log
2026/02/17 21:21 5m retest repro android13-5.15-lts report log
2026/02/01 17:17 8m retest repro android13-5.15-lts report log
2026/01/11 12:37 6m retest repro android13-5.15-lts report log
2025/12/28 08:38 6m retest repro android13-5.15-lts report log
2025/12/28 08:38 10m retest repro android13-5.15-lts report log
2025/12/09 20:48 14m retest repro android13-5.15-lts report log
2025/12/09 20:48 15m 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:
loop2: detected capacity change from 0 to 256
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:523:38
shift exponent 116 is too large for 32-bit type 'int'
CPU: 0 PID: 367 Comm: syz.2.19 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 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:523 [inline]
 __exfat_fill_super fs/exfat/super.c:579 [inline]
 exfat_fill_super+0x2964/0x2d20 fs/exfat/super.c:647
 get_tree_bdev+0x436/0x680 fs/super.c:1325
 exfat_get_tree+0x1c/0x20 fs/exfat/super.c:719
 vfs_get_tree+0x89/0x260 fs/super.c:1530
 do_new_mount+0x25a/0xa20 fs/namespace.c:3034
 path_mount+0x659/0xff0 fs/namespace.c:3364
 do_mount fs/namespace.c:3377 [inline]
 __do_sys_mount fs/namespace.c:3585 [inline]
 __se_sys_mount+0x320/0x390 fs/namespace.c:3562
 __x64_sys_mount+0xbf/0xd0 fs/namespace.c:3562
 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: 0033:0x7f000281ea0a
Code: 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f000267fe58 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f000267fee0 RCX: 00007f000281ea0a
RDX: 00002000000005c0 RSI: 0000200000000240 RDI: 00007f000267fea0
RBP: 00002000000005c0 R08: 00007f000267fee0 R09: 0000000003800052
R10: 0000000003800052 R11: 0000000000000246 R12: 0000200000000240
R13: 00007f000267fea0 R14: 00000000000014fe R15: 0000200000000600
 </TASK>
================================================================================
exFAT-fs (loop2): unable to set blocksize 1048576
exFAT-fs (loop2): failed to read boot sector
exFAT-fs (loop2): failed to recognize exfat type

Crashes (16):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/07 20:13 android13-5.15-lts f55534477be4 5cb44a80 .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
2026/03/01 19:08 android13-5.15-lts e714749f59d3 43249bac .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
2026/02/24 05:27 android13-5.15-lts 13d6d33696ef 41d2fa6a .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
2025/12/14 05:38 android13-5.15-lts 057fdbf6d3c7 d6526ea3 .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
2025/12/14 04:56 android13-5.15-lts 057fdbf6d3c7 d6526ea3 .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
2025/10/27 00:23 android13-5.15-lts 1edb21e89ce4 c0460fcd .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 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
2025/11/08 19:27 android13-5.15-lts 8a8f52308945 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/10/26 21:10 android13-5.15-lts 1edb21e89ce4 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/10/04 13:48 android13-5.15-lts 2bbc293701f8 49379ee0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-15 UBSAN: shift-out-of-bounds in exfat_fill_super
2025/09/15 15:56 android13-5.15-lts 8d934e0056f7 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] 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.