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BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
Read of size 4 at addr ffff88804bffed18 by task syz.0.0/5335

CPU: 0 UID: 0 PID: 5335 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 ext4_ext_binsearch fs/ext4/extents.c:841 [inline]
 ext4_find_extent+0xae6/0xcc0 fs/ext4/extents.c:956
 ext4_ext_map_blocks+0x288/0x6ac0 fs/ext4/extents.c:4208
 ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
 ext4_map_blocks+0x860/0x1740 fs/ext4/inode.c:811
 _ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:910
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:943
 ext4_block_write_begin+0x993/0x1710 fs/ext4/inode.c:1198
 ext4_block_page_mkwrite fs/ext4/inode.c:6643 [inline]
 ext4_page_mkwrite+0x760/0x1190 fs/ext4/inode.c:6746
 do_page_mkwrite+0x14d/0x310 mm/memory.c:3489
 wp_page_shared mm/memory.c:3890 [inline]
 do_wp_page+0x268d/0x5800 mm/memory.c:4109
 handle_pte_fault mm/memory.c:6211 [inline]
 __handle_mm_fault+0x1033/0x5400 mm/memory.c:6336
 handle_mm_fault+0x40a/0x8e0 mm/memory.c:6505
 do_user_addr_fault+0xa7c/0x1380 arch/x86/mm/fault.c:1336
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x82/0x100 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7fe6eed58e4c
Code: 00 00 00 74 a0 83 f9 c0 0f 87 56 fe ff ff 62 e1 fe 28 6f 4e 01 48 29 fe 48 83 c7 3f 49 8d 0c 10 48 83 e7 c0 48 01 fe 48 29 f9 <f3> a4 62 c1 fe 28 7f 00 62 c1 fe 28 7f 48 01 c3 0f 1f 40 00 4c 8b
RSP: 002b:00007ffe48a9a9f8 EFLAGS: 00010206
RAX: 000020000000f400 RBX: 0000000000000004 RCX: 0000000000001509
RDX: 0000000000005109 RSI: 00007fe6ee803537 RDI: 0000200000013000
RBP: 00007ffe48a9aac8 R08: 000020000000f400 R09: 0000000000000002
R10: 0000000000000000 R11: 0000000000000002 R12: 00007fe6eefe5fac
R13: 00007fe6eefe5fa0 R14: fffffffffffffffe R15: 0000000000000005
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4bffe
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
raw: 04fff00000000000 ffffea00012fffc8 ffffea00012fff48 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffff88804bffec00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804bffec80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804bffed00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88804bffed80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804bffee00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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