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BUG: KASAN: use-after-free in ext4_ext_remove_space+0x3211/0x42f0
Read of size 4 at addr ffff8880370f1c18 by task syz-executor/8252

CPU: 0 UID: 0 PID: 8252 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 print_report+0xca/0x240
 kasan_report+0x118/0x150
 ext4_ext_remove_space+0x3211/0x42f0
 ext4_ext_truncate+0x17e/0x300
 ext4_truncate+0x9c0/0x1100
 ext4_evict_inode+0x8cf/0xee0
 evict+0x504/0x9c0
 do_unlinkat+0x39f/0x560
 __x64_sys_unlink+0x47/0x50
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7e7ad8e157
Code: 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 57 00 00 00 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:00007fff7543f938 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f7e7ad8e157
RDX: 00007fff7543f960 RSI: 00007fff7543f9f0 RDI: 00007fff7543f9f0
RBP: 00007fff7543f9f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000206 R12: 00007fff75440ae0
R13: 00007f7e7ae11c05 R14: 000000000003a2fd R15: 00007fff75441bb0
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x12 pfn:0x370f1
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 dead000000000100 dead000000000122 0000000000000000
raw: 0000000000000012 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 9785, tgid 9784 (syz.6.524), ts 235104903799, free_ts 236044002777
 post_alloc_hook+0x240/0x2a0
 get_page_from_freelist+0x21e4/0x22c0
 __alloc_frozen_pages_noprof+0x181/0x370
 alloc_pages_mpol+0x232/0x4a0
 folio_alloc_mpol_noprof+0x39/0x70
 shmem_alloc_and_add_folio+0x447/0xf60
 shmem_get_folio_gfp+0x59d/0x1660
 shmem_write_begin+0xf7/0x2b0
 generic_perform_write+0x2c5/0x900
 shmem_file_write_iter+0xf8/0x120
 vfs_write+0x5c9/0xb30
 ksys_write+0x145/0x250
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 8252 tgid 8252 stack trace:
 free_unref_folios+0xdbd/0x1520
 folios_put_refs+0x559/0x640
 shmem_undo_range+0x49e/0x14b0
 shmem_evict_inode+0x272/0xa70
 evict+0x504/0x9c0
 __dentry_kill+0x209/0x660
 dput+0x19f/0x2b0
 __fput+0x68e/0xa70
 task_work_run+0x1d4/0x260
 exit_to_user_mode_loop+0xec/0x110
 do_syscall_64+0x2bd/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff8880370f1b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880370f1b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880370f1c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff8880370f1c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8880370f1d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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