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

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Message-ID: <67a23341.050a0220.163cdc.006a.GAE@google.com>
Date: Tue, 04 Feb 2025 07:33:21 -0800
From: syzbot <syzbot+fe375f77ba1a6ab944b6@...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 xas_create

Hello,

syzbot found the following issue on:

HEAD commit:    0de63bb7d919 Merge tag 'pull-fix' of git://git.kernel.org/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132078a4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1909f2f0d8e641ce
dashboard link: https://syzkaller.appspot.com/bug?extid=fe375f77ba1a6ab944b6
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=17eca3df980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10974f64580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-0de63bb7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1142009a30a7/vmlinux-0de63bb7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5d9e46a8998d/bzImage-0de63bb7.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/e651a39ab132/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fe375f77ba1a6ab944b6@...kaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in lib/xarray.c:147:16
shift exponent 252 is too large for 64-bit type 'unsigned long'
CPU: 0 UID: 0 PID: 11 Comm: kworker/u4:0 Not tainted 6.14.0-rc1-syzkaller-00020-g0de63bb7d919 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: loop0 loop_rootcg_workfn
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
 get_offset lib/xarray.c:147 [inline]
 xas_descend lib/xarray.c:207 [inline]
 xas_create+0x1832/0x1ae0 lib/xarray.c:695
 xas_store+0x96/0x1870 lib/xarray.c:794
 shmem_add_to_page_cache+0x89d/0xcc0 mm/shmem.c:897
 shmem_alloc_and_add_folio+0x968/0x1090 mm/shmem.c:1928
 shmem_get_folio_gfp+0x621/0x1840 mm/shmem.c:2522
 shmem_get_folio mm/shmem.c:2628 [inline]
 shmem_write_begin+0x165/0x350 mm/shmem.c:3278
 generic_perform_write+0x346/0x990 mm/filemap.c:4189
 shmem_file_write_iter+0xf9/0x120 mm/shmem.c:3454
 do_iter_readv_writev+0x71a/0x9d0
 vfs_iter_write+0x23e/0x600 fs/read_write.c:974
 lo_write_bvec drivers/block/loop.c:245 [inline]
 lo_write_simple drivers/block/loop.c:266 [inline]
 do_req_filebacked drivers/block/loop.c:520 [inline]
 loop_handle_cmd drivers/block/loop.c:1929 [inline]
 loop_process_work+0x1429/0x21c0 drivers/block/loop.c:1964
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317
 worker_thread+0x870/0xd30 kernel/workqueue.c:3398
 kthread+0x7a9/0x920 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
---[ end trace ]---


---
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