[syzbot] [ext4?] KASAN: use-after-free Read in ext4_ext_insert_extent

syzbot
2025-05-25T18:12:31Z

Hello,

syzbot found the following issue on:

HEAD commit: d0c22de9995b Merge tag 'input-for-v6.15-rc7' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e00df4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a1de0d8596cea805
dashboard link: https://syzkaller.appspot.com/bug?extid=9db318d6167044609878
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16931170580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14683ad4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cf852e5656de/disk-d0c22de9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/761933abe01b/vmlinux-d0c22de9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/187857154891/bzImage-d0c22de9.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/992dec4e0af9/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=151468e8580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9db318d6167044609878@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2084
Read of size 4 at addr ffff88802db31c18 by task syz-executor706/7034

CPU: 1 UID: 0 PID: 7034 Comm: syz-executor706 Not tainted 6.15.0-rc7-syzkaller-00152-gd0c22de9995b #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:408 [inline]
print_report+0xb4/0x290 mm/kasan/report.c:521
kasan_report+0x118/0x150 mm/kasan/report.c:634
ext4_ext_insert_extent+0x41b6/0x4af0 fs/ext4/extents.c:2084
ext4_ext_map_blocks+0x179c/0x67c0 fs/ext4/extents.c:4400
ext4_map_create_blocks fs/ext4/inode.c:520 [inline]
ext4_map_blocks+0x807/0x1740 fs/ext4/inode.c:706
_ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:785
ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:818
ext4_block_write_begin+0x543/0x1290 fs/ext4/inode.c:1067
ext4_write_begin+0x6f6/0x12c0 fs/ext4/ext4_jbd2.h:-1
ext4_da_write_begin+0x33a/0xa60 fs/ext4/inode.c:2932
generic_perform_write+0x2c4/0x910 mm/filemap.c:4103
ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
new_sync_write fs/read_write.c:591 [inline]
vfs_write+0x54b/0xa90 fs/read_write.c:684
ksys_pwrite64 fs/read_write.c:791 [inline]
__do_sys_pwrite64 fs/read_write.c:799 [inline]
__se_sys_pwrite64 fs/read_write.c:796 [inline]
__x64_sys_pwrite64+0x193/0x220 fs/read_write.c:796
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0078162e09
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 b1 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0078117218 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f00781ea6c8 RCX: 00007f0078162e09
RDX: 000000000000fdef RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007f00781ea6c0 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000fecc R11: 0000000000000246 R12: 00007f00781b7630
R13: 0000200000000000 R14: 00002000000000c0 R15: 00007f00781b706b
</TASK>

Allocated by task 5844:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
unpoison_slab_object mm/kasan/common.c:319 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4147 [inline]
slab_alloc_node mm/slub.c:4196 [inline]
kmem_cache_alloc_noprof+0x1c1/0x3c0 mm/slub.c:4203
getname_flags+0xb8/0x540 fs/namei.c:146
getname include/linux/fs.h:2852 [inline]
__do_sys_symlink fs/namei.c:4770 [inline]
__se_sys_symlink fs/namei.c:4768 [inline]
__x64_sys_symlink+0x6a/0x90 fs/namei.c:4768
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5844:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:247 [inline]
__kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2380 [inline]
slab_free mm/slub.c:4642 [inline]
kmem_cache_free+0x192/0x3f0 mm/slub.c:4744
do_symlinkat+0x39f/0x3f0 fs/namei.c:4757
__do_sys_symlink fs/namei.c:4770 [inline]
__se_sys_symlink fs/namei.c:4768 [inline]
__x64_sys_symlink+0x7a/0x90 fs/namei.c:4768
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802db31100
which belongs to the cache names_cache of size 4096
The buggy address is located 2840 bytes inside of
freed 4096-byte region [ffff88802db31100, ffff88802db32100)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2db30
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b2b8780 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000070007 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b2b8780 0000000000000000 dead000000000001
head: 0000000000000000 0000000000070007 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0000b6cc01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5844, tgid 5844 (udevd), ts 111781614645, free_ts 111672478666
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1d8/0x230 mm/page_alloc.c:1714
prep_new_page mm/page_alloc.c:1722 [inline]
get_page_from_freelist+0x21c7/0x22a0 mm/page_alloc.c:3684
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4966
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2301
alloc_slab_page mm/slub.c:2450 [inline]
allocate_slab+0x8a/0x3b0 mm/slub.c:2618
new_slab mm/slub.c:2672 [inline]
___slab_alloc+0xbfc/0x1480 mm/slub.c:3858
__slab_alloc mm/slub.c:3948 [inline]
__slab_alloc_node mm/slub.c:4023 [inline]
slab_alloc_node mm/slub.c:4184 [inline]
kmem_cache_alloc_noprof+0x283/0x3c0 mm/slub.c:4203
getname_flags+0xb8/0x540 fs/namei.c:146
getname include/linux/fs.h:2852 [inline]
__do_sys_symlink fs/namei.c:4770 [inline]
__se_sys_symlink fs/namei.c:4768 [inline]
__x64_sys_symlink+0x5d/0x90 fs/namei.c:4768
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5189 tgid 5189 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1258 [inline]
__free_frozen_pages+0xb05/0xcd0 mm/page_alloc.c:2721
discard_slab mm/slub.c:2716 [inline]
__put_partials+0x161/0x1c0 mm/slub.c:3185
put_cpu_partial+0x17c/0x250 mm/slub.c:3260
__slab_free+0x2f7/0x400 mm/slub.c:4512
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x9a/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:329
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4147 [inline]
slab_alloc_node mm/slub.c:4196 [inline]
__do_kmalloc_node mm/slub.c:4326 [inline]
__kmalloc_noprof+0x224/0x4f0 mm/slub.c:4339
kmalloc_noprof include/linux/slab.h:909 [inline]
tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:2377
vfs_getattr fs/stat.c:256 [inline]
vfs_fstat fs/stat.c:278 [inline]
__do_sys_newfstat fs/stat.c:546 [inline]
__se_sys_newfstat fs/stat.c:543 [inline]
__x64_sys_newfstat+0xfe/0x200 fs/stat.c:543
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88802db31b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88802db31b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88802db31c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88802db31c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88802db31d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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