==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:827 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:946
Read of size 4 at addr ffff888139c40018 by task syz.3.914/3771

CPU: 0 PID: 3771 Comm: syz.3.914 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0xf1/0x140 mm/kasan/report.c:444
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 ext4_ext_binsearch fs/ext4/extents.c:827 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:946
 ext4_ext_map_blocks+0x207/0x61e0 fs/ext4/extents.c:4172
 ext4_map_blocks+0x3b4/0x1b30 fs/ext4/inode.c:601
 ext4_iomap_alloc fs/ext4/inode.c:3432 [inline]
 ext4_iomap_begin+0x746/0xac0 fs/ext4/inode.c:3482
 iomap_iter+0x57d/0xaf0 fs/iomap/iter.c:74
 __iomap_dio_rw+0x100e/0x1a20 fs/iomap/direct-io.c:601
 iomap_dio_rw+0x3e/0x90 fs/iomap/direct-io.c:688
 ext4_dio_write_iter fs/ext4/file.c:542 [inline]
 ext4_file_write_iter+0xec8/0x1540 fs/ext4/file.c:662
 do_iter_readv_writev+0x478/0x5f0 fs/read_write.c:-1
 do_iter_write+0x1fa/0x7b0 fs/read_write.c:855
 vfs_writev+0x2df/0x570 fs/read_write.c:928
 do_pwritev fs/read_write.c:1025 [inline]
 __do_sys_pwritev2 fs/read_write.c:1084 [inline]
 __se_sys_pwritev2+0x1af/0x2b0 fs/read_write.c:1075
 __x64_sys_pwritev2+0xbf/0xd0 fs/read_write.c:1075
 x64_sys_call+0x346/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:329
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f2a12ffd819
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:00007f2a11a58028 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007f2a13276fa0 RCX: 00007f2a12ffd819
RDX: 0000000000000001 RSI: 0000200000000240 RDI: 0000000000000009
RBP: 00007f2a13093c91 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000002000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2a13277038 R14: 00007f2a13276fa0 R15: 00007fff5fa49298
 </TASK>

The buggy address belongs to the page:
page:ffffea0004e71000 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x100 pfn:0x139c40
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea0004f5ca08 ffffea0004f11808 0000000000000000
raw: 0000000000000100 0000000000000003 00000000ffffff7f 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 0x100cca(GFP_HIGHUSER_MOVABLE), pid 3741, ts 244920422182, free_ts 245438522772
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
 get_page_from_freelist+0x2d3a/0x2dc0 mm/page_alloc.c:4485
 __alloc_pages+0x1a2/0x460 mm/page_alloc.c:5822
 __alloc_pages_node include/linux/gfp.h:595 [inline]
 alloc_pages_node include/linux/gfp.h:609 [inline]
 alloc_pages include/linux/gfp.h:622 [inline]
 shmem_alloc_page mm/shmem.c:1587 [inline]
 shmem_alloc_and_acct_page+0x4a2/0x8d0 mm/shmem.c:1612
 shmem_getpage_gfp+0xfe5/0x2310 mm/shmem.c:1908
 shmem_getpage mm/shmem.c:152 [inline]
 shmem_fallocate+0x882/0xd20 mm/shmem.c:2760
 vfs_fallocate+0x4b4/0x590 fs/open.c:309
 ksys_fallocate fs/open.c:332 [inline]
 __do_sys_fallocate fs/open.c:340 [inline]
 __se_sys_fallocate fs/open.c:338 [inline]
 __x64_sys_fallocate+0xc0/0x110 fs/open.c:338
 x64_sys_call+0x7ec/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:286
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1472 [inline]
 free_pcp_prepare mm/page_alloc.c:1544 [inline]
 free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
 free_unref_page_list+0x13a/0x9d0 mm/page_alloc.c:3671
 release_pages+0x1006/0x1060 mm/swap.c:1015
 __pagevec_release+0x71/0xe0 mm/swap.c:1035
 pagevec_release include/linux/pagevec.h:81 [inline]
 shmem_undo_range+0x595/0x1470 mm/shmem.c:965
 shmem_fallocate+0xc06/0xd20 mm/shmem.c:2765
 vfs_fallocate+0x4b4/0x590 fs/open.c:309
 ksys_fallocate fs/open.c:332 [inline]
 __do_sys_fallocate fs/open.c:340 [inline]
 __se_sys_fallocate fs/open.c:338 [inline]
 __x64_sys_fallocate+0xc0/0x110 fs/open.c:338
 x64_sys_call+0x7ec/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:286
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Memory state around the buggy address:
 ffff888139c3ff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888139c3ff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888139c40000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888139c40080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888139c40100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop3): ext4_ext_split:1074: inode #15: comm syz.3.914: p_ext > EXT_MAX_EXTENT!
EXT4-fs error (device loop3): mb_free_blocks:1874: group 0, inode 15: block 337:freeing already freed block (bit 21); block bitmap corrupt.