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BUG: KASAN: use-after-free in ext4_ext_rm_leaf fs/ext4/extents.c:2602 [inline]
BUG: KASAN: use-after-free in ext4_ext_remove_space+0x33ef/0x44c0 fs/ext4/extents.c:2940
Read of size 4 at addr ffff88804fdb1c18 by task syz.0.323/5705

CPU: 0 PID: 5705 Comm: syz.0.323 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 ext4_ext_rm_leaf fs/ext4/extents.c:2602 [inline]
 ext4_ext_remove_space+0x33ef/0x44c0 fs/ext4/extents.c:2940
 ext4_ext_truncate+0x211/0x370 fs/ext4/extents.c:4470
 ext4_truncate+0xa23/0x1240 fs/ext4/inode.c:4295
 ext4_setattr+0x10cb/0x19f0 fs/ext4/inode.c:5649
 notify_change+0xc74/0xf40 fs/attr.c:499
 do_truncate+0x1ac/0x240 fs/open.c:65
 vfs_truncate+0x262/0x2f0 fs/open.c:111
 do_sys_truncate+0xf2/0x1c0 fs/open.c:134
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa48879c629
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:00007fa4869f6028 EFLAGS: 00000246 ORIG_RAX: 000000000000004c
RAX: ffffffffffffffda RBX: 00007fa488a16090 RCX: 00007fa48879c629
RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000200000000180
RBP: 00007fa488832b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa488a16128 R14: 00007fa488a16090 R15: 00007ffdb3a44d68
 </TASK>

The buggy address belongs to the physical page:
page:ffffea00013f6c40 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x4fdb1
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
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 5671, tgid 5671 (syz.2.311), ts 263092615690, free_ts 267856415022
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2559
 prep_new_page mm/page_alloc.c:2566 [inline]
 get_page_from_freelist+0x1a1e/0x1ab0 mm/page_alloc.c:4357
 __alloc_pages+0x1ec/0x4f0 mm/page_alloc.c:5643
 __folio_alloc+0xe/0x30 mm/page_alloc.c:5675
 vma_alloc_folio+0x4a3/0x900 mm/mempolicy.c:2243
 shmem_alloc_folio mm/shmem.c:1589 [inline]
 shmem_alloc_and_acct_folio+0x463/0xbc0 mm/shmem.c:1613
 shmem_get_folio_gfp+0x1361/0x3400 mm/shmem.c:1941
 shmem_get_folio mm/shmem.c:2072 [inline]
 shmem_write_begin+0xee/0x3f0 mm/shmem.c:2556
 generic_perform_write+0x2fa/0x5c0 mm/filemap.c:3862
 __generic_file_write_iter+0x148/0x2a0 mm/filemap.c:3960
 generic_file_write_iter+0xab/0x2e0 mm/filemap.c:3989
 __kernel_write_iter+0x285/0x650 fs/read_write.c:517
 dump_emit_page fs/coredump.c:950 [inline]
 dump_user_range+0x412/0x850 fs/coredump.c:977
 elf_core_dump+0x30a6/0x35d0 fs/binfmt_elf.c:2354
 do_coredump+0x165b/0x22f0 fs/coredump.c:824
 get_signal+0x10aa/0x1350 kernel/signal.c:2857
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1486 [inline]
 free_pcp_prepare mm/page_alloc.c:1536 [inline]
 free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3413
 free_unref_page_list+0xbb/0x8e0 mm/page_alloc.c:3554
 release_pages+0x1fa6/0x2220 mm/swap.c:1035
 __pagevec_release+0x6d/0xe0 mm/swap.c:1055
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x7c2/0x20c0 mm/shmem.c:946
 shmem_truncate_range mm/shmem.c:1062 [inline]
 shmem_evict_inode+0x25b/0xa80 mm/shmem.c:1171
 evict+0x4c9/0x8d0 fs/inode.c:705
 do_unlinkat+0x388/0x580 fs/namei.c:4405
 __do_sys_unlink fs/namei.c:4446 [inline]
 __se_sys_unlink fs/namei.c:4444 [inline]
 __x64_sys_unlink+0x45/0x50 fs/namei.c:4444
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff88804fdb1b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804fdb1b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804fdb1c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88804fdb1c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804fdb1d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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