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BUG: KASAN: use-after-free in ext4_ext_rm_leaf fs/ext4/extents.c:2630 [inline]
BUG: KASAN: use-after-free in ext4_ext_remove_space+0x3170/0x4280 fs/ext4/extents.c:2964
Read of size 4 at addr ffff888050659c18 by task syz.2.278/6977

CPU: 0 UID: 0 PID: 6977 Comm: syz.2.278 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/27/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ext4_ext_rm_leaf fs/ext4/extents.c:2630 [inline]
 ext4_ext_remove_space+0x3170/0x4280 fs/ext4/extents.c:2964
 ext4_ext_truncate+0x17e/0x2f0 fs/ext4/extents.c:4537
 ext4_truncate+0xb63/0x13b0 fs/ext4/inode.c:4567
 ext4_setattr+0x106e/0x1c60 fs/ext4/inode.c:5959
 notify_change+0xc1a/0xf40 fs/attr.c:556
 do_truncate+0x1c2/0x250 fs/open.c:68
 handle_truncate fs/namei.c:4301 [inline]
 do_open fs/namei.c:4697 [inline]
 path_openat+0x2f89/0x3860 fs/namei.c:4852
 do_file_open+0x23e/0x4a0 fs/namei.c:4881
 do_sys_openat2+0x113/0x200 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_open fs/open.c:1380 [inline]
 __se_sys_open fs/open.c:1376 [inline]
 __x64_sys_open+0x11e/0x150 fs/open.c:1376
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7eff2939c799
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:00007eff275b4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007eff29616180 RCX: 00007eff2939c799
RDX: 00000000000000dc RSI: 000000000004827e RDI: 0000200000000200
RBP: 00007eff29432c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007eff29616218 R14: 00007eff29616180 R15: 00007ffc4de741e8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x32a0 pfn:0x50659
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001419608 ffffea0001419688 0000000000000000
raw: 00000000000032a0 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 6936, tgid 6936 (syz.1.266), ts 185088332446, free_ts 190652221220
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1857
 prep_new_page mm/page_alloc.c:1865 [inline]
 get_page_from_freelist+0x2418/0x24b0 mm/page_alloc.c:3924
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5211
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2484
 folio_alloc_mpol_noprof+0x39/0x160 mm/mempolicy.c:2503
 shmem_alloc_folio mm/shmem.c:1933 [inline]
 shmem_alloc_and_add_folio+0x442/0xf80 mm/shmem.c:1975
 shmem_get_folio_gfp+0x5a9/0x1670 mm/shmem.c:2564
 shmem_get_folio mm/shmem.c:2670 [inline]
 shmem_write_begin+0x16c/0x330 mm/shmem.c:3323
 generic_perform_write+0x2e2/0x8f0 mm/filemap.c:4319
 shmem_file_write_iter+0xf8/0x120 mm/shmem.c:3498
 __kernel_write_iter+0x41e/0x880 fs/read_write.c:621
 dump_emit_page fs/coredump.c:1299 [inline]
 dump_user_range+0xc19/0x12c0 fs/coredump.c:1373
 elf_core_dump+0x34c2/0x3ad0 fs/binfmt_elf.c:2110
 coredump_write+0x1216/0x1910 fs/coredump.c:1050
 do_coredump fs/coredump.c:1127 [inline]
 vfs_coredump+0x36a9/0x4280 fs/coredump.c:1201
 get_signal+0x1107/0x1330 kernel/signal.c:3020
page last free pid 5830 tgid 5830 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1401 [inline]
 free_unref_folios+0xd0c/0x1450 mm/page_alloc.c:3003
 folios_put_refs+0x9ff/0xb40 mm/swap.c:1008
 folio_batch_release include/linux/folio_batch.h:101 [inline]
 shmem_undo_range+0x52c/0x1660 mm/shmem.c:1149
 shmem_truncate_range mm/shmem.c:1277 [inline]
 shmem_evict_inode+0x289/0xae0 mm/shmem.c:1407
 evict+0x61e/0xb10 fs/inode.c:846
 filename_unlinkat+0x43f/0x610 fs/namei.c:5566
 __do_sys_unlink fs/namei.c:5597 [inline]
 __se_sys_unlink+0x2e/0x140 fs/namei.c:5594
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888050659b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888050659b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888050659c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888050659c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888050659d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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