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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff8880408f0018 by task syz.6.235/8804

CPU: 1 UID: 0 PID: 8804 Comm: syz.6.235 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
 ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
 ext4_ext_map_blocks+0x29d/0x6b80 fs/ext4/extents.c:4208
 ext4_map_create_blocks fs/ext4/inode.c:613 [inline]
 ext4_map_blocks+0x8da/0x1830 fs/ext4/inode.c:816
 _ext4_get_block+0x1e3/0x470 fs/ext4/inode.c:916
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:949
 ext4_block_write_begin+0xb14/0x1950 fs/ext4/inode.c:1203
 ext4_write_begin+0xb40/0x1870 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x355/0xd30 fs/ext4/inode.c:3130
 generic_perform_write+0x2af/0x8b0 mm/filemap.c:4314
 ext4_buffered_write_iter+0xd0/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x299/0x1c20 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x629/0xba0 fs/read_write.c:686
 ksys_write+0x156/0x270 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7700c7aeb9
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:00007f76feed6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f7700ef5fa0 RCX: 00007f7700c7aeb9
RDX: 00000000ffffff6a RSI: 0000200000000000 RDI: 0000000000000006
RBP: 00007f7700ce8c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7700ef6038 R14: 00007f7700ef5fa0 R15: 00007ffd6f31e7a8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xc54 pfn:0x408f0
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea0000fca3c8 ffffea0001023c48 0000000000000000
raw: 0000000000000c54 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 8731, tgid 8730 (syz.3.296), ts 423406045883, free_ts 423944959751
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x228/0x280 mm/page_alloc.c:1884
 prep_new_page mm/page_alloc.c:1892 [inline]
 get_page_from_freelist+0x28bb/0x2950 mm/page_alloc.c:3945
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5240
 alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x39/0xe0 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1913 [inline]
 shmem_alloc_and_add_folio mm/shmem.c:1955 [inline]
 shmem_get_folio_gfp+0x644/0x1a80 mm/shmem.c:2579
 shmem_get_folio mm/shmem.c:2685 [inline]
 shmem_write_begin+0x166/0x320 mm/shmem.c:3338
 generic_perform_write+0x2af/0x8b0 mm/filemap.c:4314
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:3513
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x629/0xba0 fs/read_write.c:686
 ksys_write+0x156/0x270 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 8731 tgid 8730 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1433 [inline]
 free_unref_folios+0xd5e/0x19d0 mm/page_alloc.c:3030
 folios_put_refs+0x56f/0x680 mm/swap.c:1002
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x52e/0x1670 mm/shmem.c:1149
 shmem_truncate_range mm/shmem.c:1272 [inline]
 shmem_evict_inode+0x240/0x9e0 mm/shmem.c:1402
 evict+0x61e/0xb10 fs/inode.c:837
 __dentry_kill+0x1a2/0x5e0 fs/dcache.c:670
 finish_dput+0xc9/0x480 fs/dcache.c:879
 __fput+0x6a0/0xa80 fs/file_table.c:476
 fput_close_sync+0x11f/0x240 fs/file_table.c:573
 __do_sys_close fs/open.c:1573 [inline]
 __se_sys_close fs/open.c:1558 [inline]
 __x64_sys_close+0x7e/0x110 fs/open.c:1558
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff8880408eff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880408eff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880408f0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff8880408f0080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880408f0100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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