[v6.6] KASAN: vmalloc-out-of-bounds Read in xfs_buf_lock

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4fc00fe35d46 Linux 6.6.129
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=121c5e16580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=de5ae0fe914bc0ecf264
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b69a43016252/disk-4fc00fe3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/240ac8d2cf70/vmlinux-4fc00fe3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/67c7958e5edb/bzImage-4fc00fe3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+de5ae0...@syzkaller.appspotmail.com

binder: 10780:10781 ioctl c0306201 0 returned -14
syz.7.988 (10781): drop_caches: 2
==================================================================
BUG: KASAN: vmalloc-out-of-bounds in xfs_buf_lock+0x22c/0x460 fs/xfs/xfs_buf.c:1124
Read of size 4 at addr ffffc9001505f8fc by task syz.7.988/10781

CPU: 1 PID: 10781 Comm: syz.7.988 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:468
kasan_report+0x117/0x150 mm/kasan/report.c:581
xfs_buf_lock+0x22c/0x460 fs/xfs/xfs_buf.c:1124
xfs_buf_delwri_submit_buffers+0x15f/0x890 fs/xfs/xfs_buf.c:2210
xfs_buf_delwri_submit+0xc5/0x250 fs/xfs/xfs_buf.c:2288
xfs_qm_shrink_scan+0x1a7/0x3a0 fs/xfs/xfs_qm.c:522
do_shrink_slab+0x50f/0xd10 mm/vmscan.c:907
shrink_slab+0x1d0/0x7f0 mm/vmscan.c:1067
drop_slab_node mm/vmscan.c:1095 [inline]
drop_slab+0x15b/0x2a0 mm/vmscan.c:1113
drop_caches_sysctl_handler+0xc7/0x170 fs/drop_caches.c:68
proc_sys_call_handler+0x463/0x6d0 fs/proc/proc_sysctl.c:599
do_iter_readv_writev fs/read_write.c:-1 [inline]
do_iter_write+0x738/0xc30 fs/read_write.c:860
iter_file_splice_write+0x6a3/0xcb0 fs/splice.c:736
do_splice_from fs/splice.c:933 [inline]
direct_splice_actor+0xe8/0x130 fs/splice.c:1142
splice_direct_to_actor+0x304/0x8c0 fs/splice.c:1088
do_splice_direct+0x1d5/0x2f0 fs/splice.c:1194
do_sendfile+0x5f2/0xef0 fs/read_write.c:1254
__do_sys_sendfile64 fs/read_write.c:1316 [inline]
__se_sys_sendfile64+0xe0/0x1a0 fs/read_write.c:1308
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6f4b99c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007f6f4c864028 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f6f4bc15fa0 RCX: 00007f6f4b99c799
RDX: 0000200000002080 RSI: 0000000000000003 RDI: 0000000000000007
RBP: 00007f6f4ba32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000012 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6f4bc16038 R14: 00007f6f4bc15fa0 R15: 00007ffff2d02098
</TASK>

The buggy address belongs to a 8-page vmalloc region starting at 0xffffc90015058000 allocated at copy_process+0x586/0x3d80 kernel/fork.c:2331
The buggy address belongs to the physical page:
page:ffffea0001f1b4c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7c6d3
memcg:ffff888141677e02
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff ffff888141677e02
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x102dc2(GFP_HIGHUSER|__GFP_NOWARN|__GFP_ZERO), pid 2, tgid 2 (kthreadd), ts 548846047594, free_ts 444145841340
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1581
prep_new_page mm/page_alloc.c:1588 [inline]
get_page_from_freelist+0x1951/0x19e0 mm/page_alloc.c:3220
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4500
vm_area_alloc_pages mm/vmalloc.c:3089 [inline]
__vmalloc_area_node mm/vmalloc.c:3158 [inline]
__vmalloc_node_range+0x956/0x1330 mm/vmalloc.c:3339
alloc_thread_stack_node kernel/fork.c:310 [inline]
dup_task_struct+0x3d0/0x7c0 kernel/fork.c:1124
copy_process+0x586/0x3d80 kernel/fork.c:2331
kernel_clone+0x24b/0x8a0 kernel/fork.c:2914
kernel_thread+0x13f/0x1b0 kernel/fork.c:2976
create_kthread kernel/kthread.c:411 [inline]
kthreadd+0x57f/0x750 kernel/kthread.c:766
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1181 [inline]
free_unref_page_prepare+0x7b2/0x8c0 mm/page_alloc.c:2365
free_unref_page+0x32/0x2e0 mm/page_alloc.c:2458
kasan_depopulate_vmalloc_pte+0x75/0x90 mm/kasan/shadow.c:427
apply_to_pte_range mm/memory.c:2604 [inline]
apply_to_pmd_range mm/memory.c:2648 [inline]
apply_to_pud_range mm/memory.c:2684 [inline]
apply_to_p4d_range mm/memory.c:2720 [inline]
__apply_to_page_range+0x860/0xdd0 mm/memory.c:2756
kasan_release_vmalloc+0x97/0xb0 mm/kasan/shadow.c:544
__purge_vmap_area_lazy+0xfa7/0x1af0 mm/vmalloc.c:1778
drain_vmap_area_work+0x40/0xd0 mm/vmalloc.c:1812
process_one_work kernel/workqueue.c:2653 [inline]
process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2730
worker_thread+0xa55/0xfc0 kernel/workqueue.c:2811
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Memory state around the buggy address:
ffffc9001505f780: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
ffffc9001505f800: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc9001505f880: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
^
ffffc9001505f900: f3 f3 f3 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00
ffffc9001505f980: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
==================================================================


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