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BUG: KASAN: use-after-free in ext4_ext_correct_indexes+0x72/0x5b0 fs/ext4/extents.c:1712
Read of size 8 at addr ffff8880296ac050 by task syz.2.800/9968

CPU: 0 UID: 0 PID: 9968 Comm: syz.2.800 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ext4_ext_correct_indexes+0x72/0x5b0 fs/ext4/extents.c:1712
 ext4_ext_insert_extent+0x2007/0x4b50 fs/ext4/extents.c:2188
 ext4_ext_map_blocks+0x1a72/0x6b80 fs/ext4/extents.c:4404
 ext4_map_create_blocks fs/ext4/inode.c:613 [inline]
 ext4_map_blocks+0x8da/0x1830 fs/ext4/inode.c:816
 _ext4_get_block+0x1e3/0x470 fs/ext4/inode.c:916
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:949
 ext4_block_write_begin+0xb14/0x1950 fs/ext4/inode.c:1203
 ext4_write_begin+0xb40/0x1870 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x355/0xd30 fs/ext4/inode.c:3130
 generic_perform_write+0x2af/0x8b0 mm/filemap.c:4314
 ext4_buffered_write_iter+0xd0/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x299/0x1c20 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x629/0xba0 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x19c/0x230 fs/read_write.c:798
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5601f490b9
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:00007f56011a6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f5602175fa0 RCX: 00007f5601f490b9
RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007f5601fdb9c4 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000fecc R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f5602175fa0 R15: 00007ffc90a6fc88
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x296ac
flags: 0x80000000000000(node=0|zone=1)
page_type: f0(buddy)
raw: 0080000000000000 ffffea0000c77208 ffffea0000eac408 0000000000000000
raw: 0000000000000000 0000000000000002 00000000f0000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x440dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_COMP), pid 6329, tgid 6329 (syz-executor), ts 231102599294, free_ts 231411799571
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x228/0x280 mm/page_alloc.c:1884
 prep_new_page mm/page_alloc.c:1892 [inline]
 get_page_from_freelist+0x28bb/0x2950 mm/page_alloc.c:3945
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5240
 alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2486
 alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
 alloc_pages_noprof+0xce/0x1e0 mm/mempolicy.c:2577
 pagetable_alloc_noprof include/linux/mm.h:3190 [inline]
 __pte_alloc_one_noprof include/asm-generic/pgalloc.h:76 [inline]
 pte_alloc_one+0x23/0x380 arch/x86/mm/pgtable.c:18
 __pte_alloc+0x25/0x1a0 mm/memory.c:453
 copy_pte_range mm/memory.c:1237 [inline]
 copy_pmd_range+0x71e2/0x7a00 mm/memory.c:1392
 copy_pud_range mm/memory.c:1429 [inline]
 copy_p4d_range mm/memory.c:1453 [inline]
 copy_page_range+0xaf9/0x1120 mm/memory.c:1535
 dup_mmap+0xf7c/0x1b70 mm/mmap.c:1827
 dup_mm kernel/fork.c:1529 [inline]
 copy_mm+0x13b/0x4b0 kernel/fork.c:1581
 copy_process+0x16db/0x3a90 kernel/fork.c:2221
 kernel_clone+0x249/0x7f0 kernel/fork.c:2651
 __do_sys_clone kernel/fork.c:2792 [inline]
 __se_sys_clone kernel/fork.c:2776 [inline]
 __x64_sys_clone+0x1b6/0x230 kernel/fork.c:2776
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 20 tgid 20 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xfc1/0x1130 mm/page_alloc.c:2973
 __tlb_remove_table_free mm/mmu_gather.c:227 [inline]
 tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:290
 rcu_do_batch kernel/rcu/tree.c:2605 [inline]
 rcu_core kernel/rcu/tree.c:2857 [inline]
 rcu_cpu_kthread+0xbba/0x1b10 kernel/rcu/tree.c:2945
 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
 kthread+0x726/0x8b0 kernel/kthread.c:463
 ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Memory state around the buggy address:
 ffff8880296abf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880296abf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880296ac000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                 ^
 ffff8880296ac080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880296ac100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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