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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+0xb92/0xd80 fs/ext4/extents.c:955
Read of size 4 at addr ffff8880508788e8 by task syz.2.173/6799

CPU: 1 UID: 0 PID: 6799 Comm: syz.2.173 Not tainted 6.15.0-rc2-syzkaller-00042-g1a1d569a75f3 #0 PREEMPT(full) 
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+0xb92/0xd80 fs/ext4/extents.c:955
 ext4_ext_map_blocks+0x2e6/0x7d80 fs/ext4/extents.c:4205
 ext4_map_query_blocks+0x97/0x2c0 fs/ext4/inode.c:472
 ext4_map_blocks+0x3e3/0x1920 fs/ext4/inode.c:670
 _ext4_get_block+0x23b/0x6b0 fs/ext4/inode.c:785
 ext4_get_block_unwritten+0x2f/0x100 fs/ext4/inode.c:818
 ext4_block_write_begin+0x4da/0x1520 fs/ext4/inode.c:1067
 ext4_write_begin+0x786/0x1330 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x4aa/0xb20 fs/ext4/inode.c:2932
 generic_perform_write+0x32b/0xa10 mm/filemap.c:4102
 ext4_buffered_write_iter+0xc7/0x390 fs/ext4/file.c:299
 ext4_file_write_iter+0x97f/0x1da0 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x711/0xd10 fs/read_write.c:684
 ksys_write+0x19d/0x2d0 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6b7878e169
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:00007f6b7960a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6b789b5fa0 RCX: 00007f6b7878e169
RDX: 0000000000010010 RSI: 0000200000000080 RDI: 000000000000000f
RBP: 00007f6b78810a68 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f6b789b5fa0 R15: 00007ffc6ba94ec8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xee8 pfn:0x50878
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000ee8 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 6741, tgid 6740 (syz.4.164), ts 189819316346, free_ts 190890327877
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f4/0x240 mm/page_alloc.c:1717
 prep_new_page mm/page_alloc.c:1725 [inline]
 get_page_from_freelist+0x352b/0x36c0 mm/page_alloc.c:3652
 __alloc_frozen_pages_noprof+0x211/0x5b0 mm/page_alloc.c:4934
 alloc_pages_mpol+0x339/0x690 mm/mempolicy.c:2301
 folio_alloc_mpol_noprof+0x36/0x70 mm/mempolicy.c:2320
 shmem_alloc_folio mm/shmem.c:1854 [inline]
 shmem_alloc_and_add_folio+0x490/0x1070 mm/shmem.c:1893
 shmem_get_folio_gfp+0x655/0x1800 mm/shmem.c:2533
 shmem_get_folio mm/shmem.c:2639 [inline]
 shmem_write_begin+0x17e/0x3a0 mm/shmem.c:3289
 generic_perform_write+0x32b/0xa10 mm/filemap.c:4102
 shmem_file_write_iter+0xf9/0x120 mm/shmem.c:3464
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x711/0xd10 fs/read_write.c:684
 ksys_write+0x19d/0x2d0 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5843 tgid 5843 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1262 [inline]
 free_unref_folios+0xe0e/0x17f0 mm/page_alloc.c:2737
 folios_put_refs+0x70a/0x800 mm/swap.c:992
 folio_batch_release include/linux/pagevec.h:101 [inline]
 shmem_undo_range+0x595/0x1820 mm/shmem.c:1125
 shmem_truncate_range mm/shmem.c:1237 [inline]
 shmem_evict_inode+0x29d/0xa80 mm/shmem.c:1365
 evict+0x4fb/0x9b0 fs/inode.c:810
 __dentry_kill+0x20d/0x630 fs/dcache.c:660
 dput+0x19f/0x2b0 fs/dcache.c:902
 __fput+0x60b/0x9f0 fs/file_table.c:473
 task_work_run+0x253/0x310 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 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+0x13f/0x340 kernel/entry/common.c:218
 do_syscall_64+0x100/0x230 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888050878780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888050878800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888050878880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                          ^
 ffff888050878900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888050878980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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