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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 ffff88805ea9e20c by task syz.0.627/9104

CPU: 0 UID: 0 PID: 9104 Comm: syz.0.627 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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_ext_binsearch fs/ext4/extents.c:841 [inline]
 ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
 ext4_ext_map_blocks+0x288/0x6ac0 fs/ext4/extents.c:4208
 ext4_map_query_blocks+0x13b/0x930 fs/ext4/inode.c:549
 ext4_map_blocks+0x4b3/0x1740 fs/ext4/inode.c:772
 _ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:909
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:942
 ext4_block_write_begin+0x993/0x1710 fs/ext4/inode.c:1197
 ext4_write_begin+0xb47/0x1880 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x352/0xd50 fs/ext4/inode.c:3125
 generic_perform_write+0x29d/0x8c0 mm/filemap.c:4300
 ext4_buffered_write_iter+0xd0/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x299/0x1be0 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5d5/0xb40 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x196/0x220 fs/read_write.c:798
 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: 0033:0x7f02fbf7f749
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:00007f02fb5ee038 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f02fc1d5fa0 RCX: 00007f02fbf7f749
RDX: 00000000200000c1 RSI: 00002000000000c0 RDI: 0000000000000004
RBP: 00007f02fc003f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000009000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f02fc1d6038 R14: 00007f02fc1d5fa0 R15: 00007ffe5f9857c8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x5a0 pfn:0x5ea9e
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 dead000000000100 dead000000000122 0000000000000000
raw: 00000000000005a0 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 9084, tgid 9083 (syz.2.623), ts 668366836102, free_ts 668872863397
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1845
 prep_new_page mm/page_alloc.c:1853 [inline]
 get_page_from_freelist+0x28c0/0x2960 mm/page_alloc.c:3879
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5178
 alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2416
 folio_alloc_mpol_noprof+0x39/0xe0 mm/mempolicy.c:2435
 shmem_alloc_folio mm/shmem.c:1870 [inline]
 shmem_alloc_and_add_folio mm/shmem.c:1912 [inline]
 shmem_get_folio_gfp+0x633/0x1a70 mm/shmem.c:2535
 shmem_get_folio mm/shmem.c:2641 [inline]
 shmem_write_begin+0xef/0x2a0 mm/shmem.c:3291
 generic_perform_write+0x29d/0x8c0 mm/filemap.c:4300
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:3466
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5d5/0xb40 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x196/0x220 fs/read_write.c:798
 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
page last free pid 5986 tgid 5986 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 free_unref_folios+0xc22/0x1860 mm/page_alloc.c:2958
 folios_put_refs+0x569/0x670 mm/swap.c:1002
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x49e/0x1490 mm/shmem.c:1119
 shmem_truncate_range mm/shmem.c:1231 [inline]
 shmem_evict_inode+0x272/0xa70 mm/shmem.c:1359
 evict+0x5f4/0xae0 fs/inode.c:837
 do_unlinkat+0x39f/0x570 fs/namei.c:4814
 __do_sys_unlink fs/namei.c:4853 [inline]
 __se_sys_unlink fs/namei.c:4851 [inline]
 __x64_sys_unlink+0x47/0x50 fs/namei.c:4851
 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

Memory state around the buggy address:
 ffff88805ea9e100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88805ea9e180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88805ea9e200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff88805ea9e280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88805ea9e300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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