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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+0xb61/0xd50 fs/ext4/extents.c:955
Read of size 4 at addr ffff88806ae85e18 by task syz.4.39/6240

CPU: 0 UID: 0 PID: 6240 Comm: syz.4.39 Not tainted 6.14.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0x16e/0x5b0 mm/kasan/report.c:521
 kasan_report+0x143/0x180 mm/kasan/report.c:634
 ext4_ext_binsearch fs/ext4/extents.c:840 [inline]
 ext4_find_extent+0xb61/0xd50 fs/ext4/extents.c:955
 ext4_ext_map_blocks+0x2e4/0x7d30 fs/ext4/extents.c:4205
 ext4_map_create_blocks fs/ext4/inode.c:516 [inline]
 ext4_map_blocks+0x8bf/0x1990 fs/ext4/inode.c:702
 _ext4_get_block+0x239/0x6b0 fs/ext4/inode.c:781
 ext4_get_block_unwritten+0x2f/0x100 fs/ext4/inode.c:814
 __block_write_begin_int+0x692/0x19a0 fs/buffer.c:2116
 block_page_mkwrite+0x3ad/0x520 fs/buffer.c:2629
 ext4_page_mkwrite+0x462/0x1100 fs/ext4/inode.c:6236
 do_page_mkwrite+0x15c/0x350 mm/memory.c:3257
 wp_page_shared mm/memory.c:3658 [inline]
 do_wp_page+0x23cd/0x49b0 mm/memory.c:3808
 handle_pte_fault mm/memory.c:5923 [inline]
 __handle_mm_fault+0x24d5/0x70f0 mm/memory.c:6050
 handle_mm_fault+0x2c1/0x7e0 mm/memory.c:6219
 do_user_addr_fault arch/x86/mm/fault.c:1337 [inline]
 handle_page_fault arch/x86/mm/fault.c:1480 [inline]
 exc_page_fault+0x459/0x8b0 arch/x86/mm/fault.c:1538
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
RIP: 0033:0x7ff406b54eab
Code: fa 10 73 2d 83 fa 08 73 46 83 fa 04 73 16 83 fa 01 7c 10 8a 0e 74 0a 0f b7 74 16 fe 66 89 74 17 fe 88 0f c3 8b 4c 16 fc 8b 36 <89> 4c 17 fc 89 37 c3 c5 fa 6f 06 c5 fa 6f 4c 16 f0 c5 fa 7f 07 c5
RSP: 002b:00007ffe42df9eb8 EFLAGS: 00010206
RAX: 0000400000001540 RBX: 0000000000000004 RCX: 00000000676f6c65
RDX: 0000000000000007 RSI: 0000000065657274 RDI: 0000400000001540
RBP: 00007ff406da7ba0 R08: 00007ff406a00000 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000009 R12: 00007ff406da5fac
R13: 00007ff406da5fa0 R14: fffffffffffffffe R15: 00007ffe42df9fd0
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xbe9 pfn:0x6ae85
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001aba188 ffffea0001aba108 0000000000000000
raw: 0000000000000be9 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 6241, tgid 6240 (syz.4.39), ts 106200722436, free_ts 106512992908
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1551
 prep_new_page mm/page_alloc.c:1559 [inline]
 get_page_from_freelist+0x3651/0x37a0 mm/page_alloc.c:3477
 __alloc_frozen_pages_noprof+0x292/0x710 mm/page_alloc.c:4740
 alloc_pages_mpol+0x311/0x660 mm/mempolicy.c:2270
 folio_alloc_mpol_noprof+0x36/0x70 mm/mempolicy.c:2289
 shmem_alloc_folio mm/shmem.c:1863 [inline]
 shmem_alloc_and_add_folio+0x4a0/0x1090 mm/shmem.c:1902
 shmem_get_folio_gfp+0x621/0x1840 mm/shmem.c:2545
 shmem_get_folio mm/shmem.c:2651 [inline]
 shmem_write_begin+0x165/0x350 mm/shmem.c:3301
 generic_perform_write+0x346/0x990 mm/filemap.c:4188
 shmem_file_write_iter+0xf9/0x120 mm/shmem.c:3477
 new_sync_write fs/read_write.c:586 [inline]
 vfs_write+0xacf/0xd10 fs/read_write.c:679
 ksys_write+0x18f/0x2b0 fs/read_write.c:731
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 6241 tgid 6240 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 free_unref_folios+0xe2f/0x18a0 mm/page_alloc.c:2707
 folios_put_refs+0x76c/0x860 mm/swap.c:994
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x593/0x1820 mm/shmem.c:1112
 shmem_truncate_range mm/shmem.c:1224 [inline]
 shmem_evict_inode+0x29b/0xa80 mm/shmem.c:1352
 evict+0x4e8/0x9a0 fs/inode.c:796
 __dentry_kill+0x20d/0x630 fs/dcache.c:643
 dput+0x19f/0x2b0 fs/dcache.c:885
 __fput+0x60b/0x9f0 fs/file_table.c:472
 __do_sys_close fs/open.c:1580 [inline]
 __se_sys_close fs/open.c:1565 [inline]
 __x64_sys_close+0x7f/0x110 fs/open.c:1565
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88806ae85d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806ae85d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88806ae85e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88806ae85e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88806ae85f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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