[moderation] [ext4?] KASAN: use-after-free Read in ext4_xattr_list_entries

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c746c3b51698 Merge tag 'for-6.18-tag' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=104e7334580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c1486b135ff0ff9b
dashboard link: https://syzkaller.appspot.com/bug?extid=e572868a12a792912c89
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-c746c3b5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8de5aa0a3f80/vmlinux-c746c3b5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/797705bd8ae3/bzImage-c746c3b5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e57286...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 2048
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: none.
EXT4-fs error (device loop0): ext4_mb_generate_buddy:1289: group 0, block bitmap and bg descriptor inconsistent: 25 vs 150994969 free clusters
EXT4-fs (loop0): Delayed block allocation failed for inode 18 at logical offset 0 with max blocks 752 with error 28
EXT4-fs (loop0): This should not happen!! Data will be lost
EXT4-fs (loop0): Total free blocks count 0
EXT4-fs (loop0): Free/Dirty block details
EXT4-fs (loop0): free_blocks=2415919104
EXT4-fs (loop0): dirty_blocks=768
EXT4-fs (loop0): Block reservation details
EXT4-fs (loop0): i_reserved_data_blocks=48
==================================================================
BUG: KASAN: use-after-free in ext4_xattr_list_entries+0x302/0x3d0 fs/ext4/xattr.c:724
Read of size 4 at addr ffff88800093c014 by task syz.0.0/5322

CPU: 0 UID: 0 PID: 5322 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
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_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
ext4_xattr_list_entries+0x302/0x3d0 fs/ext4/xattr.c:724
ext4_xattr_ibody_list fs/ext4/xattr.c:793 [inline]
ext4_listxattr+0x1f9/0x630 fs/ext4/xattr.c:818
vfs_listxattr fs/xattr.c:493 [inline]
listxattr+0x10f/0x2a0 fs/xattr.c:924
filename_listxattr fs/xattr.c:958 [inline]
path_listxattrat+0x179/0x3a0 fs/xattr.c:988
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7f8f58eec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7f90343038 EFLAGS: 00000246 ORIG_RAX: 00000000000000c3
RAX: ffffffffffffffda RBX: 00007f7f8f7e5fa0 RCX: 00007f7f8f58eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000500
RBP: 00007f7f8f611f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7f8f7e6038 R14: 00007f7f8f7e5fa0 R15: 00007ffcdd84be88
</TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xa0 pfn:0x93c
flags: 0x7ff00000000000(node=0|zone=0|lastcpupid=0x7ff)
page_type: f0(buddy)
raw: 007ff00000000000 ffffea0000025508 ffffea0000024308 0000000000000000
raw: 00000000000000a0 0000000000000002 00000000f0000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x152c4a(GFP_NOFS|__GFP_HIGHMEM|__GFP_MOVABLE|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 4721, tgid 4721 (udevadm), ts 26354988631, free_ts 73610747374
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
prep_new_page mm/page_alloc.c:1858 [inline]
get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3884
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5183
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_frozen_pages_noprof mm/mempolicy.c:2487 [inline]
alloc_pages_noprof+0xa9/0x190 mm/mempolicy.c:2507
folio_alloc_noprof+0x1e/0x30 mm/mempolicy.c:2517
filemap_alloc_folio_noprof+0xdf/0x470 mm/filemap.c:1020
ractl_alloc_folio mm/readahead.c:189 [inline]
page_cache_ra_unbounded+0x35d/0x9a0 mm/readahead.c:275
do_async_mmap_readahead mm/filemap.c:3376 [inline]
filemap_fault+0x62d/0x12b0 mm/filemap.c:3475
__do_fault+0x138/0x390 mm/memory.c:5280
do_read_fault mm/memory.c:5698 [inline]
do_fault mm/memory.c:5832 [inline]
do_pte_missing mm/memory.c:4361 [inline]
handle_pte_fault mm/memory.c:6177 [inline]
__handle_mm_fault+0x35e3/0x5400 mm/memory.c:6318
handle_mm_fault+0x40a/0x8e0 mm/memory.c:6487
do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
handle_page_fault arch/x86/mm/fault.c:1476 [inline]
exc_page_fault+0x82/0x100 arch/x86/mm/fault.c:1532
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
page last free pid 78 tgid 78 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1394 [inline]
free_unref_folios+0xdb3/0x14f0 mm/page_alloc.c:2963
shrink_folio_list+0x295e/0x4c70 mm/vmscan.c:1569
evict_folios+0x471e/0x57c0 mm/vmscan.c:4745
try_to_shrink_lruvec+0x8a3/0xb50 mm/vmscan.c:4908
shrink_one+0x21b/0x7c0 mm/vmscan.c:4953
shrink_many mm/vmscan.c:5016 [inline]
lru_gen_shrink_node mm/vmscan.c:5094 [inline]
shrink_node+0x315d/0x3780 mm/vmscan.c:6081
kswapd_shrink_node mm/vmscan.c:6941 [inline]
balance_pgdat mm/vmscan.c:7124 [inline]
kswapd+0x147c/0x2800 mm/vmscan.c:7389
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
ffff88800093bf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88800093bf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88800093c000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88800093c080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88800093c100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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