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BUG: KASAN: use-after-free in strcmp+0x6b/0xc0 lib/string.c:265
Read of size 1 at addr ffff88804197e8a6 by task syz.2.51/6074

CPU: 1 UID: 0 PID: 6074 Comm: syz.2.51 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 strcmp+0x6b/0xc0 lib/string.c:265
 hpfs_get_ea+0x137/0xeb0 fs/hpfs/ea.c:139
 hpfs_read_inode+0x1a9/0x1060 fs/hpfs/inode.c:63
 hpfs_fill_super+0x1275/0x1fa0 fs/hpfs/super.c:652
 get_tree_bdev_flags+0x430/0x4f0 fs/super.c:1873
 vfs_get_tree+0x92/0x2a0 fs/super.c:1933
 fc_mount fs/namespace.c:1198 [inline]
 do_new_mount_fc fs/namespace.c:3772 [inline]
 do_new_mount+0x319/0xdc0 fs/namespace.c:3848
 do_mount fs/namespace.c:4181 [inline]
 __do_sys_mount fs/namespace.c:4397 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4374
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f149e50f3ca
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:00007f149c765e58 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f149c765ee0 RCX: 00007f149e50f3ca
RDX: 000020000000a000 RSI: 0000200000009ec0 RDI: 00007f149c765ea0
RBP: 000020000000a000 R08: 00007f149c765ee0 R09: 0000000003a00041
R10: 0000000003a00041 R11: 0000000000000246 R12: 0000200000009ec0
R13: 00007f149c765ea0 R14: 0000000000009e22 R15: 0000200000000080
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x28 pfn:0x4197e
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea0001065fc8 ffffea0001065f48 0000000000000000
raw: 0000000000000028 0000000000000000 00000000ffffffff 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 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 6019, tgid 6017 (syz.3.43), ts 123650900616
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x2591/0x2600 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x230/0x5c0 mm/page_alloc.c:5436
 alloc_pages_mpol+0xd4/0x280 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x3b/0x1e0 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1933 [inline]
 shmem_alloc_and_add_folio mm/shmem.c:1975 [inline]
 shmem_get_folio_gfp+0x6ee/0x1c40 mm/shmem.c:2528
 shmem_get_folio mm/shmem.c:2634 [inline]
 shmem_write_begin+0x166/0x320 mm/shmem.c:3265
 generic_perform_write+0x2ad/0x8b0 mm/filemap.c:4374
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:3440
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x61e/0xbb0 fs/read_write.c:687
 ksys_write+0x156/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 6017 tgid 6017 ts 125543378555 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 free_unref_folios+0xd0f/0x1950 mm/page_alloc.c:3022
 folios_put_refs+0x815/0x920 mm/folio.c:1036
 folio_batch_release include/linux/folio_batch.h:101 [inline]
 shmem_undo_range+0x4e6/0x15d0 mm/shmem.c:1161
 shmem_truncate_range mm/shmem.c:1289 [inline]
 shmem_evict_inode+0x247/0xae0 mm/shmem.c:1420
 evict+0x624/0xb50 fs/inode.c:822
 dentry_kill+0x1b9/0x880 fs/dcache.c:826
 finish_dput+0x1a/0x260 fs/dcache.c:1001
 __fput+0x699/0xa80 fs/file_table.c:520
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x73a/0x2360 kernel/exit.c:1012
 do_group_exit+0x22d/0x2f0 kernel/exit.c:1155
 get_signal+0x121b/0x12c0 kernel/signal.c:3112
 arch_do_signal_or_restart+0xbb/0x860 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x10e/0x770 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x328/0x520 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88804197e780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804197e800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804197e880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                               ^
 ffff88804197e900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804197e980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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