==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:826 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:945
Read of size 4 at addr ffff888132fa0e18 by task syz.3.119/788

CPU: 0 PID: 788 Comm: syz.3.119 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0xe2/0x130 mm/kasan/report.c:452
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:308
 ext4_ext_binsearch fs/ext4/extents.c:826 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:945
 ext4_ext_map_blocks+0x20b/0x5dd0 fs/ext4/extents.c:4166
 ext4_map_blocks+0x985/0x1bd0 fs/ext4/inode.c:674
 mpage_map_one_extent fs/ext4/inode.c:2452 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2505 [inline]
 ext4_writepages+0x136a/0x2eb0 fs/ext4/inode.c:2873
 do_writepages+0x128/0x280 mm/page-writeback.c:2380
 __filemap_fdatawrite_range+0x2a0/0x350 mm/filemap.c:427
 file_write_and_wait_range+0x8c/0x110 mm/filemap.c:766
 ext4_sync_file+0x1a9/0x9f0 fs/ext4/fsync.c:151
 vfs_fsync_range+0x190/0x1a0 fs/sync.c:202
 generic_write_sync include/linux/fs.h:2920 [inline]
 ext4_buffered_write_iter+0x59b/0x640 fs/ext4/file.c:278
 ext4_file_write_iter+0x53f/0x1980 fs/ext4/file.c:-1
 call_write_iter include/linux/fs.h:2066 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x758/0xdc0 fs/read_write.c:605
 ksys_pwrite64 fs/read_write.c:712 [inline]
 __do_sys_pwrite64 fs/read_write.c:722 [inline]
 __se_sys_pwrite64 fs/read_write.c:719 [inline]
 __x64_sys_pwrite64+0x197/0x220 fs/read_write.c:719
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f1d4b4ad799
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:00007f1d49f08028 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f1d4b726fa0 RCX: 00007f1d4b4ad799
RDX: 00000000200000c1 RSI: 00002000000000c0 RDI: 0000000000000004
RBP: 00007f1d4b543c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000009000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1d4b727038 R14: 00007f1d4b726fa0 R15: 00007ffd3a5f2918

The buggy address belongs to the page:
page:ffffea0004cbe800 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x132fa0
flags: 0x4000000000000000()
raw: 4000000000000000 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 0x100cca(GFP_HIGHUSER_MOVABLE), pid 699, ts 45411678579, free_ts 45704733054
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x223b/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x290/0x620 mm/page_alloc.c:5384
 __alloc_pages include/linux/gfp.h:544 [inline]
 __alloc_pages_node include/linux/gfp.h:557 [inline]
 alloc_pages_node include/linux/gfp.h:571 [inline]
 alloc_pages include/linux/gfp.h:590 [inline]
 shmem_alloc_page+0x1fd/0x380 mm/shmem.c:1584
 shmem_alloc_and_acct_page+0x3b7/0x820 mm/shmem.c:1609
 shmem_getpage_gfp+0x625/0x2120 mm/shmem.c:1922
 shmem_getpage mm/shmem.c:165 [inline]
 shmem_write_begin+0xce/0x1b0 mm/shmem.c:2501
 generic_perform_write+0x2ce/0x540 mm/filemap.c:3509
 __generic_file_write_iter+0x24b/0x480 mm/filemap.c:3638
 generic_file_write_iter+0xa9/0x1d0 mm/filemap.c:3670
 __kernel_write+0x535/0x910 fs/read_write.c:550
 dump_emit+0x246/0x370 fs/coredump.c:855
 dump_user_range+0x6a/0x1a0 fs/coredump.c:908
 elf_core_dump+0x2866/0x2cc0 fs/binfmt_elf.c:2290
 do_coredump+0x1ba3/0x28e0 fs/coredump.c:817
 __seccomp_filter+0x1957/0x1b00 kernel/seccomp.c:1272
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 free_pcp_prepare mm/page_alloc.c:1421 [inline]
 free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336
 free_unref_page_list+0x129/0x9c0 mm/page_alloc.c:3443
 release_pages+0xe52/0xea0 mm/swap.c:1103
 __pagevec_release+0x71/0xe0 mm/swap.c:1123
 pagevec_release include/linux/pagevec.h:88 [inline]
 shmem_undo_range+0x74a/0x1810 mm/shmem.c:969
 shmem_truncate_range mm/shmem.c:1073 [inline]
 shmem_evict_inode+0x210/0xa00 mm/shmem.c:1173
 evict+0x4ae/0x930 fs/inode.c:612
 iput_final fs/inode.c:1736 [inline]
 iput+0x638/0x7c0 fs/inode.c:1762
 do_unlinkat+0x347/0x680 fs/namei.c:4050
 __do_sys_unlink fs/namei.c:4090 [inline]
 __se_sys_unlink fs/namei.c:4088 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4088
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Memory state around the buggy address:
 ffff888132fa0d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888132fa0d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888132fa0e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888132fa0e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888132fa0f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop3): ext4_ext_split:1073: inode #15: comm syz.3.119: p_ext > EXT_MAX_EXTENT!
EXT4-fs (loop3): Delayed block allocation failed for inode 15 at logical offset 204 with max blocks 4 with error 117
EXT4-fs (loop3): This should not happen!! Data will be lost