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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbcc/0xe00 fs/ext4/extents.c:953
Read of size 4 at addr ffff88804de9510c by task syz.0.46/4593

CPU: 1 PID: 4593 Comm: syz.0.46 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
 ext4_find_extent+0xbcc/0xe00 fs/ext4/extents.c:953
 ext4_ext_map_blocks+0x27d/0x66d0 fs/ext4/extents.c:4166
 ext4_map_blocks+0x9d1/0x1b60 fs/ext4/inode.c:679
 _ext4_get_block+0x1d7/0x4e0 fs/ext4/inode.c:822
 ext4_block_write_begin+0x637/0x12f0 fs/ext4/inode.c:1124
 ext4_write_begin+0x624/0xf50 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x304/0x950 fs/ext4/inode.c:3000
 generic_perform_write+0x2db/0x560 mm/filemap.c:3846
 ext4_buffered_write_iter+0x11a/0x3e0 fs/ext4/file.c:285
 ext4_file_write_iter+0x1d6/0x16e0 fs/ext4/file.c:-1
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x44c/0x960 fs/read_write.c:584
 ksys_write+0x143/0x240 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f485478ebe9
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:00007f48556b2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f48549b6090 RCX: 00007f485478ebe9
RDX: 00000000fffffdef RSI: 00002000000000c0 RDI: 0000000000000007
RBP: 00007f4854811e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f48549b6128 R14: 00007f48549b6090 R15: 00007fffeb2b7b48
 </TASK>

The buggy address belongs to the physical page:
page:ffffea000137a540 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x4de95
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea000137a588 ffffea000137a508 0000000000000000
raw: 0000000000000001 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 4591, tgid 4591 (syz.1.48), ts 100078845125, free_ts 100821696528
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2532
 prep_new_page mm/page_alloc.c:2539 [inline]
 get_page_from_freelist+0x1a26/0x1ac0 mm/page_alloc.c:4328
 __alloc_pages+0x1df/0x4e0 mm/page_alloc.c:5614
 __folio_alloc+0xe/0x30 mm/page_alloc.c:5646
 vma_alloc_folio+0x4a3/0x900 mm/mempolicy.c:2243
 shmem_alloc_folio mm/shmem.c:1589 [inline]
 shmem_alloc_and_acct_folio+0x42e/0xb60 mm/shmem.c:1613
 shmem_get_folio_gfp+0x1361/0x3400 mm/shmem.c:1941
 shmem_get_folio mm/shmem.c:2072 [inline]
 shmem_write_begin+0xee/0x3f0 mm/shmem.c:2556
 generic_perform_write+0x2db/0x560 mm/filemap.c:3846
 __generic_file_write_iter+0x172/0x430 mm/filemap.c:3974
 generic_file_write_iter+0xab/0x2e0 mm/filemap.c:4006
 __kernel_write_iter+0x26d/0x630 fs/read_write.c:517
 dump_emit_page fs/coredump.c:950 [inline]
 dump_user_range+0x3ea/0x7f0 fs/coredump.c:977
 elf_core_dump+0x2f77/0x3490 fs/binfmt_elf.c:2354
 do_coredump+0x15ff/0x22b0 fs/coredump.c:824
 get_signal+0x10aa/0x1350 kernel/signal.c:2857
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1459 [inline]
 free_pcp_prepare mm/page_alloc.c:1509 [inline]
 free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3384
 free_unref_page_list+0xbb/0x8e0 mm/page_alloc.c:3525
 release_pages+0x1f92/0x2200 mm/swap.c:1035
 __pagevec_release+0x6d/0xe0 mm/swap.c:1055
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x75b/0x2050 mm/shmem.c:946
 shmem_truncate_range mm/shmem.c:1062 [inline]
 shmem_evict_inode+0x248/0xa40 mm/shmem.c:1171
 evict+0x485/0x870 fs/inode.c:705
 do_unlinkat+0x377/0x560 fs/namei.c:4397
 __do_sys_unlink fs/namei.c:4438 [inline]
 __se_sys_unlink fs/namei.c:4436 [inline]
 __x64_sys_unlink+0x45/0x50 fs/namei.c:4436
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff88804de95000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804de95080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804de95100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff88804de95180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804de95200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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