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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:826 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:945
Read of size 4 at addr ffff888135c7a8e8 by task syz.7.219/1114

CPU: 0 PID: 1114 Comm: syz.7.219 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0xe2/0x130 mm/kasan/report.c:452
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 ext4_ext_binsearch fs/ext4/extents.c:826 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:945
 ext4_ext_map_blocks+0x20b/0x5dd0 fs/ext4/extents.c:4166
 ext4_map_blocks+0x3b1/0x1bd0 fs/ext4/inode.c:601
 ext4_mpage_readpages+0xa05/0x2110 fs/ext4/readpage.c:343
 ext4_readahead+0xe4/0x110 fs/ext4/inode.c:3352
 read_pages+0x17b/0xb60 mm/readahead.c:140
 page_cache_ra_unbounded+0x42c/0x7e0 mm/readahead.c:222
 do_page_cache_ra+0xf2/0x110 mm/readahead.c:277
 do_sync_mmap_readahead mm/filemap.c:2668 [inline]
 filemap_fault+0x1211/0x20d0 mm/filemap.c:2811
 ext4_filemap_fault+0x8a/0xa0 fs/ext4/inode.c:6412
 __do_fault mm/memory.c:4064 [inline]
 do_shared_fault mm/memory.c:4453 [inline]
 do_fault mm/memory.c:4531 [inline]
 handle_pte_fault+0x13e3/0x3750 mm/memory.c:4791
 __handle_mm_fault mm/memory.c:4944 [inline]
 handle_mm_fault+0xf81/0x1710 mm/memory.c:5358
 do_user_addr_fault+0x5a8/0xc90 arch/x86/mm/fault.c:1362
 handle_page_fault arch/x86/mm/fault.c:1428 [inline]
 exc_page_fault+0x5a/0xc0 arch/x86/mm/fault.c:1484
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:571
RIP: 0033:0x7f6180b91f25
Code: 48 8b 04 24 48 85 c0 74 17 48 8b 74 24 10 48 0f ce 48 89 74 24 10 48 83 f8 01 0f 85 f0 02 00 00 48 8b 44 24 18 48 8b 54 24 10 <48> 89 10 e9 5a fe ff ff 48 8b 44 24 20 48 0b 44 24 28 75 30 48 8b
RSP: 002b:00007ffcc0333150 EFLAGS: 00010246
RAX: 0000200000000c40 RBX: 0000000000000008 RCX: 0000000000000000
RDX: 00000000000000ec RSI: 0000000000000000 RDI: 0000555574eec3d8
RBP: 00007ffcc0333270 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000000000ec R11: 0000000000000001 R12: 00007ffcc03332b0
R13: 00007f6180f41fac R14: 000000000000bed0 R15: 00007f6180f41fa0

The buggy address belongs to the page:
page:ffffea0004d71e80 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x135c7a
flags: 0x4000000000000000()
raw: 4000000000000000 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 0x100cca(GFP_HIGHUSER_MOVABLE), pid 1100, ts 48654481513, free_ts 48873074255
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x223b/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x290/0x620 mm/page_alloc.c:5384
 __alloc_pages include/linux/gfp.h:544 [inline]
 __alloc_pages_node include/linux/gfp.h:557 [inline]
 alloc_pages_node include/linux/gfp.h:571 [inline]
 alloc_pages include/linux/gfp.h:590 [inline]
 shmem_alloc_page+0x1fd/0x380 mm/shmem.c:1580
 shmem_alloc_and_acct_page+0x3b7/0x820 mm/shmem.c:1605
 shmem_getpage_gfp+0x625/0x2120 mm/shmem.c:1918
 shmem_getpage mm/shmem.c:161 [inline]
 shmem_write_begin+0xce/0x1b0 mm/shmem.c:2497
 generic_perform_write+0x2ce/0x540 mm/filemap.c:3509
 __generic_file_write_iter+0x24b/0x480 mm/filemap.c:3638
 generic_file_write_iter+0xa9/0x1d0 mm/filemap.c:3670
 call_write_iter include/linux/fs.h:2066 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x758/0xdc0 fs/read_write.c:605
 ksys_write+0x149/0x250 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 free_pcp_prepare mm/page_alloc.c:1421 [inline]
 free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336
 free_unref_page_list+0x129/0x9c0 mm/page_alloc.c:3443
 release_pages+0xe52/0xea0 mm/swap.c:1103
 __pagevec_release+0x71/0xe0 mm/swap.c:1123
 pagevec_release include/linux/pagevec.h:88 [inline]
 shmem_undo_range+0x74a/0x1810 mm/shmem.c:965
 shmem_truncate_range mm/shmem.c:1069 [inline]
 shmem_evict_inode+0x210/0xa00 mm/shmem.c:1169
 evict+0x4ae/0x930 fs/inode.c:612
 iput_final fs/inode.c:1736 [inline]
 iput+0x638/0x7c0 fs/inode.c:1762
 dentry_unlink_inode+0x2cf/0x380 fs/dcache.c:378
 __dentry_kill+0x44f/0x650 fs/dcache.c:583
 dentry_kill+0xc0/0x2a0 fs/dcache.c:-1
 dput+0x42/0x80 fs/dcache.c:883
 __fput+0x4fe/0x770 fs/file_table.c:294
 ____fput+0x15/0x20 fs/file_table.c:314
 task_work_run+0x127/0x190 kernel/task_work.c:189
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop+0xcb/0xe0 kernel/entry/common.c:172

Memory state around the buggy address:
 ffff888135c7a780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888135c7a800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888135c7a880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                          ^
 ffff888135c7a900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888135c7a980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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