==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
Read of size 4 at addr ffff888146e18c4c by task syz.2.787/3087

CPU: 1 PID: 3087 Comm: syz.2.787 Tainted: G        W          syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x71/0x200 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:420
 kasan_report+0x122/0x150 mm/kasan/report.c:524
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:350
 ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
 ext4_ext_map_blocks+0x207/0x61d0 fs/ext4/extents.c:4166
 ext4_map_blocks+0x9d8/0x1b70 fs/ext4/inode.c:679
 mpage_map_one_extent fs/ext4/inode.c:2435 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2488 [inline]
 ext4_writepages+0x1409/0x30e0 fs/ext4/inode.c:2856
 do_writepages+0x3a4/0x5f0 mm/page-writeback.c:2494
 filemap_fdatawrite_wbc+0x128/0x190 mm/filemap.c:408
 __filemap_fdatawrite_range mm/filemap.c:441 [inline]
 file_write_and_wait_range+0x159/0x230 mm/filemap.c:794
 ext4_sync_file+0x1a9/0xa10 fs/ext4/fsync.c:151
 vfs_fsync_range+0x1a1/0x1b0 fs/sync.c:188
 generic_write_sync include/linux/fs.h:2980 [inline]
 ext4_buffered_write_iter+0x573/0x630 fs/ext4/file.c:292
 ext4_file_write_iter+0x191/0x1500 fs/ext4/file.c:-1
 call_write_iter include/linux/fs.h:2282 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x603/0xce0 fs/read_write.c:584
 ksys_write+0x149/0x250 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:646
 x64_sys_call+0x27b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fbef7f9bf79
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:00007fbef8e8d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fbef8215fa0 RCX: 00007fbef7f9bf79
RDX: 000000000208e24b RSI: 0000200000000000 RDI: 0000000000000005
RBP: 00007fbef80327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbef8216038 R14: 00007fbef8215fa0 R15: 00007ffde32a18d8
 </TASK>

The buggy address belongs to the physical page:
page:ffffea00051b8600 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x1 pfn:0x146e18
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea00051dba08 ffffea00051e5808 0000000000000000
raw: 0000000000000001 0000000000000003 00000000ffffff7f 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 3048, tgid 3048 (syz.3.772), ts 150620436244, free_ts 151068668862
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2643
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2650
 get_page_from_freelist+0x2d12/0x2d80 mm/page_alloc.c:4554
 __alloc_pages+0x1d9/0x480 mm/page_alloc.c:5868
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5900
 __folio_alloc_node include/linux/gfp.h:245 [inline]
 folio_alloc include/linux/gfp.h:274 [inline]
 shmem_alloc_folio mm/shmem.c:1601 [inline]
 shmem_alloc_and_acct_folio+0x6dd/0x8c0 mm/shmem.c:1626
 shmem_get_folio_gfp+0x119f/0x2230 mm/shmem.c:1955
 shmem_get_folio mm/shmem.c:2086 [inline]
 shmem_write_begin+0xea/0x2c0 mm/shmem.c:2571
 generic_perform_write+0x32d/0x740 mm/filemap.c:3903
 __generic_file_write_iter+0x17a/0x230 mm/filemap.c:4002
 generic_file_write_iter+0xae/0x310 mm/filemap.c:4031
 __kernel_write_iter+0x296/0x660 fs/read_write.c:517
 dump_emit_page fs/coredump.c:886 [inline]
 dump_user_range+0x40b/0x660 fs/coredump.c:913
 elf_core_dump+0x2b52/0x3060 fs/binfmt_elf.c:2354
 do_coredump+0x15d3/0x2240 fs/coredump.c:760
 get_signal+0x11db/0x1520 kernel/signal.c:2877
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1551 [inline]
 free_pcp_prepare mm/page_alloc.c:1625 [inline]
 free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3589
 free_unref_page_list+0x117/0x8c0 mm/page_alloc.c:3740
 release_pages+0xaf2/0xb50 mm/swap.c:1048
 __pagevec_release+0x71/0xe0 mm/swap.c:1068
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x574/0x1540 mm/shmem.c:955
 shmem_truncate_range mm/shmem.c:1071 [inline]
 shmem_evict_inode+0x255/0xa50 mm/shmem.c:1180
 evict+0x4d7/0x8f0 fs/inode.c:708
 iput_final fs/inode.c:1844 [inline]
 iput+0x620/0x670 fs/inode.c:1870
 do_unlinkat+0x380/0x6d0 fs/namei.c:4404
 __do_sys_unlink fs/namei.c:4445 [inline]
 __se_sys_unlink fs/namei.c:4443 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4443
 x64_sys_call+0x958/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff888146e18b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888146e18b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888146e18c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff888146e18c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888146e18d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs (loop2): Delayed block allocation failed for inode 18 at logical offset 0 with max blocks 1 with error 28
EXT4-fs (loop2): This should not happen!! Data will be lost

EXT4-fs (loop2): Total free blocks count 0
EXT4-fs (loop2): Free/Dirty block details
EXT4-fs (loop2): free_blocks=64
EXT4-fs (loop2): dirty_blocks=0
EXT4-fs (loop2): Block reservation details
EXT4-fs (loop2): i_reserved_data_blocks=0