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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:955
Read of size 4 at addr ffff888042658018 by task syz.0.492/11074

CPU: 1 UID: 0 PID: 11074 Comm: syz.0.492 Not tainted 6.15.0-rc7-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xb4/0x290 mm/kasan/report.c:521
 kasan_report+0x118/0x150 mm/kasan/report.c:634
 ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
 ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:955
 ext4_ext_map_blocks+0x26f/0x67c0 fs/ext4/extents.c:4205
 ext4_map_create_blocks fs/ext4/inode.c:520 [inline]
 ext4_map_blocks+0x807/0x1740 fs/ext4/inode.c:706
 _ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:785
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:818
 __block_write_begin_int+0x6b2/0x1900 fs/buffer.c:2149
 block_page_mkwrite+0x34f/0x4d0 fs/buffer.c:2644
 ext4_page_mkwrite+0x47c/0x1110 fs/ext4/inode.c:6297
 do_page_mkwrite+0x14a/0x310 mm/memory.c:3287
 wp_page_shared mm/memory.c:3688 [inline]
 do_wp_page+0x2626/0x5790 mm/memory.c:3907
 handle_pte_fault mm/memory.c:6013 [inline]
 __handle_mm_fault+0x1028/0x5380 mm/memory.c:6140
 handle_mm_fault+0x2d5/0x7f0 mm/memory.c:6309
 do_user_addr_fault+0xa81/0x1390 arch/x86/mm/fault.c:1337
 handle_page_fault arch/x86/mm/fault.c:1480 [inline]
 exc_page_fault+0x68/0x110 arch/x86/mm/fault.c:1538
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0033:0x7f5b0c556807
Code: ce 48 ff c7 48 01 fe 48 8d 54 11 80 0f 1f 80 00 00 00 00 c5 fe 6f 0e c5 fe 6f 56 20 c5 fe 6f 5e 40 c5 fe 6f 66 60 48 83 ee 80 <c5> fd 7f 0f c5 fd 7f 57 20 c5 fd 7f 5f 40 c5 fd 7f 67 60 48 83 ef
RSP: 002b:00007ffd42fd7cf8 EFLAGS: 00010203
RAX: 0000200000002800 RBX: 0000000000000004 RCX: 0000200000002800
RDX: 0000200000002f60 RSI: 00007f5b0c015e83 RDI: 0000200000002820
RBP: 00007ffd42fd7dc8 R08: 0000000000000000 R09: 000000000000001f
R10: 0000000000000000 R11: 0000000000000001 R12: 00007f5b0c7b608c
R13: 00007f5b0c7b6080 R14: fffffffffffffffe R15: 00007ffd42fd7e10
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xd06 pfn:0x42658
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000d06 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 10942, tgid 10941 (syz.3.477), ts 396410611396, free_ts 400324880161
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1d8/0x230 mm/page_alloc.c:1714
 prep_new_page mm/page_alloc.c:1722 [inline]
 get_page_from_freelist+0x21c7/0x22a0 mm/page_alloc.c:3684
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4966
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2301
 folio_alloc_mpol_noprof+0x39/0x70 mm/mempolicy.c:2320
 shmem_alloc_folio mm/shmem.c:1854 [inline]
 shmem_alloc_and_add_folio+0x447/0xf60 mm/shmem.c:1893
 shmem_get_folio_gfp+0x597/0x15f0 mm/shmem.c:2533
 shmem_get_folio mm/shmem.c:2639 [inline]
 shmem_write_begin+0xf7/0x2b0 mm/shmem.c:3289
 generic_perform_write+0x2c4/0x910 mm/filemap.c:4103
 shmem_file_write_iter+0xf8/0x120 mm/shmem.c:3464
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x54b/0xa90 fs/read_write.c:684
 ksys_write+0x145/0x250 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 9128 tgid 9128 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1258 [inline]
 free_unref_folios+0xb70/0x1490 mm/page_alloc.c:2778
 folios_put_refs+0x559/0x640 mm/swap.c:992
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x49e/0x14b0 mm/shmem.c:1125
 shmem_truncate_range mm/shmem.c:1237 [inline]
 shmem_evict_inode+0x272/0xa70 mm/shmem.c:1365
 evict+0x501/0x9c0 fs/inode.c:810
 __dentry_kill+0x209/0x660 fs/dcache.c:660
 dput+0x19f/0x2b0 fs/dcache.c:902
 __fput+0x68e/0xa70 fs/file_table.c:473
 task_work_run+0x1d4/0x260 kernel/task_work.c:227
 resume_user_mode_work+0x5e/0x80 include/linux/resume_user_mode.h:50
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x9a/0x120 kernel/entry/common.c:218
 do_syscall_64+0x103/0x210 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888042657f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888042657f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888042658000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888042658080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888042658100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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