linux-kernel - [syzbot] [mm?] [bcachefs?] UBSAN: shift-out-of-bounds in shmem_undo

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Message-ID: <67d7184f.050a0220.3657bb.0002.GAE@google.com>
Date: Sun, 16 Mar 2025 11:28:31 -0700
From: syzbot <syzbot+3ed98178a28b3ce6680c@...kaller.appspotmail.com>
To: akpm@...ux-foundation.org, hughd@...gle.com, kent.overstreet@...ux.dev, 
	linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [mm?] [bcachefs?] UBSAN: shift-out-of-bounds in shmem_undo_range

Hello,

syzbot found the following issue on:

HEAD commit:    0fed89a961ea Merge tag 'hyperv-fixes-signed-20250311' of g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13f24c78580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=31c94a07ddad0b00
dashboard link: https://syzkaller.appspot.com/bug?extid=3ed98178a28b3ce6680c
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10a61874580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-0fed89a9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9e4d0fd4258e/vmlinux-0fed89a9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ea186f3b1240/bzImage-0fed89a9.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/0ad36b250ea5/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3ed98178a28b3ce6680c@...kaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in lib/xarray.c:196:22
shift exponent 240 is too large for 64-bit type 'unsigned long'
CPU: 0 UID: 0 PID: 5449 Comm: syz-executor Not tainted 6.14.0-rc6-syzkaller-00016-g0fed89a961ea #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:231 [inline]
 __ubsan_handle_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
 xas_start+0x772/0x7b0 lib/xarray.c:196
 xas_load+0x2c/0x5c0 lib/xarray.c:239
 xas_find+0x13f/0x960 lib/xarray.c:1273
 find_get_entry mm/filemap.c:2015 [inline]
 find_lock_entries+0x269/0xbb0 mm/filemap.c:2119
 shmem_undo_range+0x2d4/0x1820 mm/shmem.c:1094
 shmem_truncate_range mm/shmem.c:1224 [inline]
 shmem_evict_inode+0x29b/0xa80 mm/shmem.c:1352
 evict+0x4e8/0x9a0 fs/inode.c:796
 __dentry_kill+0x20d/0x630 fs/dcache.c:643
 dput+0x19f/0x2b0 fs/dcache.c:885
 __fput+0x60b/0x9f0 fs/file_table.c:472
 task_work_run+0x24f/0x310 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x13f/0x340 kernel/entry/common.c:218
 do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fad4c78bdca
Code: 48 3d 00 f0 ff ff 77 48 c3 0f 1f 80 00 00 00 00 48 83 ec 18 89 7c 24 0c e8 43 91 02 00 8b 7c 24 0c 89 c2 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 36 89 d7 89 44 24 0c e8 a3 91 02 00 8b 44 24
RSP: 002b:00007fff96e49350 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 00007fad4c78bdca
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fff96e493ac R08: 0000000000000000 R09: 00007fff96e490b7
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000001
R13: 0000555594fa6590 R14: 0000000000022d85 R15: 00007fff96e49400
 </TASK>
---[ end trace ]---


---
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