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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+0xbd0/0xe00 fs/ext4/extents.c:953
Read of size 4 at addr ffff888074e7a018 by task syz.3.150/6691

CPU: 1 PID: 6691 Comm: syz.3.150 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xac/0x220 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
 ext4_find_extent+0xbd0/0xe00 fs/ext4/extents.c:953
 ext4_ext_map_blocks+0x260/0x6450 fs/ext4/extents.c:4163
 ext4_map_blocks+0x9d5/0x1b70 fs/ext4/inode.c:652
 ext4_iomap_alloc fs/ext4/inode.c:3360 [inline]
 ext4_iomap_begin+0x7be/0xad0 fs/ext4/inode.c:3410
 iomap_iter+0x6b1/0xec0 fs/iomap/iter.c:91
 __iomap_dio_rw+0xb9c/0x1c40 fs/iomap/direct-io.c:658
 iomap_dio_rw+0x45/0xa0 fs/iomap/direct-io.c:748
 ext4_dio_write_iter fs/ext4/file.c:577 [inline]
 ext4_file_write_iter+0x13ff/0x1870 fs/ext4/file.c:696
 do_iter_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x79a/0xc70 fs/read_write.c:860
 iter_file_splice_write+0x66f/0xc50 fs/splice.c:736
 do_splice_from fs/splice.c:933 [inline]
 direct_splice_actor+0xe8/0x130 fs/splice.c:1142
 splice_direct_to_actor+0x2f0/0x870 fs/splice.c:1088
 do_splice_direct+0x1b7/0x2c0 fs/splice.c:1194
 do_sendfile+0x5dc/0xf70 fs/read_write.c:1254
 __do_sys_sendfile64 fs/read_write.c:1322 [inline]
 __se_sys_sendfile64+0x13f/0x190 fs/read_write.c:1308
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f48e658f749
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:00007f48e47f6038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f48e67e5fa0 RCX: 00007f48e658f749
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 0000000000000006
RBP: 00007f48e6613f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020fffe82 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f48e67e6038 R14: 00007f48e67e5fa0 R15: 00007ffe86e57dd8
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0001d39e80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x74e7a
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000000 dead000000000100 dead000000000122 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 6680, tgid 6680 (syz.1.145), ts 152814564203, free_ts 155549099203
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
 prep_new_page mm/page_alloc.c:1561 [inline]
 get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
 __alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
 __folio_alloc+0x10/0x20 mm/page_alloc.c:4489
 vma_alloc_folio+0x47a/0x8f0 mm/mempolicy.c:2242
 shmem_alloc_folio+0x179/0x230 mm/shmem.c:1679
 shmem_alloc_and_acct_folio+0x189/0x630 mm/shmem.c:1704
 shmem_get_folio_gfp+0xcde/0x2ac0 mm/shmem.c:2041
 shmem_get_folio mm/shmem.c:2164 [inline]
 shmem_write_begin+0xf2/0x420 mm/shmem.c:2706
 generic_perform_write+0x2fb/0x5b0 mm/filemap.c:4031
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:2883
 __kernel_write_iter+0x274/0x670 fs/read_write.c:517
 dump_emit_page fs/coredump.c:957 [inline]
 dump_user_range+0x3f6/0x800 fs/coredump.c:984
 elf_core_dump+0x3114/0x36e0 fs/binfmt_elf.c:2184
 do_coredump+0x1755/0x2480 fs/coredump.c:833
 get_signal+0x1133/0x1400 kernel/signal.c:2888
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1154 [inline]
 free_unref_page_prepare+0x7ce/0x8e0 mm/page_alloc.c:2336
 free_unref_page_list+0xbe/0x860 mm/page_alloc.c:2475
 release_pages+0x1fa0/0x2220 mm/swap.c:1022
 __folio_batch_release+0x71/0xe0 mm/swap.c:1042
 folio_batch_release include/linux/pagevec.h:83 [inline]
 shmem_undo_range+0x5d0/0x1a40 mm/shmem.c:1026
 shmem_truncate_range mm/shmem.c:1135 [inline]
 shmem_evict_inode+0x273/0xa70 mm/shmem.c:1264
 evict+0x486/0x870 fs/inode.c:705
 do_unlinkat+0x37b/0x570 fs/namei.c:4406
 __do_sys_unlink fs/namei.c:4447 [inline]
 __se_sys_unlink fs/namei.c:4445 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4445
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff888074e79f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888074e79f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888074e7a000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888074e7a080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888074e7a100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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