Re: [PATCH v4] ocfs2: fix oob in __ocfs2_find_path

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 2025/12/19 18:07, Heming Zhao wrote:
> On Fri, Dec 19, 2025 at 04:31:52PM +0800, Edward Adam Davis wrote:
>> syzbot constructed a corrupted image, which resulted in el->l_count
>> from the b-tree extent block being 0. Since the length of the l_recs
>> array depends on l_count, reading its member e_blkno triggered the
>> out-of-bounds access reported by syzbot in [1].
>>
>> The loop terminates when l_count is 0, similar to when next_free is 0.
>>
>> [1]
>> UBSAN: array-index-out-of-bounds in fs/ocfs2/alloc.c:1838:11
>> index 0 is out of range for type 'struct ocfs2_extent_rec[] __counted_by(l_count)' (aka 'struct ocfs2_extent_rec[]')
>> Call Trace:
>>  __ocfs2_find_path+0x606/0xa40 fs/ocfs2/alloc.c:1838
>>  ocfs2_find_leaf+0xab/0x1c0 fs/ocfs2/alloc.c:1946
>>  ocfs2_get_clusters_nocache+0x172/0xc60 fs/ocfs2/extent_map.c:418
>>  ocfs2_get_clusters+0x505/0xa70 fs/ocfs2/extent_map.c:631
>>  ocfs2_extent_map_get_blocks+0x202/0x6a0 fs/ocfs2/extent_map.c:678
>>  ocfs2_read_virt_blocks+0x286/0x930 fs/ocfs2/extent_map.c:1001
>>  ocfs2_read_dir_block fs/ocfs2/dir.c:521 [inline]
>>  ocfs2_find_entry_el fs/ocfs2/dir.c:728 [inline]
>>  ocfs2_find_entry+0x3e4/0x2090 fs/ocfs2/dir.c:1120
>>  ocfs2_find_files_on_disk+0xdf/0x310 fs/ocfs2/dir.c:2023
>>  ocfs2_lookup_ino_from_name+0x52/0x100 fs/ocfs2/dir.c:2045
>>  _ocfs2_get_system_file_inode fs/ocfs2/sysfile.c:136 [inline]
>>  ocfs2_get_system_file_inode+0x326/0x770 fs/ocfs2/sysfile.c:112
>>  ocfs2_init_global_system_inodes+0x319/0x660 fs/ocfs2/super.c:461
>>  ocfs2_initialize_super fs/ocfs2/super.c:2196 [inline]
>>  ocfs2_fill_super+0x4432/0x65b0 fs/ocfs2/super.c:993
>>  get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
>>  vfs_get_tree+0x92/0x2a0 fs/super.c:1751
>>  fc_mount fs/namespace.c:1199 [inline]
>>
>> Reported-by: syzbot+151afab124dfbc5f15e6@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=151afab124dfbc5f15e6
>> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> 
> LGTM.
> Reviewed-by: Heming Zhao <heming.zhao@suse.com>

Acked-by: Joseph Qi <joseph.qi@linux.alibaba.com>
>> ---
>> v3 -> v4: update comments
>> v2 -> v3: remove le16 and Fix tag and update comments
>> v1 -> v2: check l_count and update comments
>>
>>  fs/ocfs2/alloc.c | 9 +++++----
>>  1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
>> index 58bf58b68955..b7db177d17d6 100644
>> --- a/fs/ocfs2/alloc.c
>> +++ b/fs/ocfs2/alloc.c
>> @@ -1812,14 +1812,15 @@ static int __ocfs2_find_path(struct ocfs2_caching_info *ci,
>>  			ret = -EROFS;
>>  			goto out;
>>  		}
>> -		if (le16_to_cpu(el->l_next_free_rec) == 0) {
>> +		if (!el->l_next_free_rec || !el->l_count) {
>>  			ocfs2_error(ocfs2_metadata_cache_get_super(ci),
>> -				    "Owner %llu has empty extent list at depth %u\n",
>> +				    "Owner %llu has empty extent list at depth %u\n"
>> +				    "(next free=%u count=%u)\n",
>>  				    (unsigned long long)ocfs2_metadata_cache_owner(ci),
>> -				    le16_to_cpu(el->l_tree_depth));
>> +				    le16_to_cpu(el->l_tree_depth),
>> +				    le16_to_cpu(el->l_next_free_rec), le16_to_cpu(el->l_count));
>>  			ret = -EROFS;
>>  			goto out;
>> -
>>  		}
>>  
>>  		for(i = 0; i < le16_to_cpu(el->l_next_free_rec) - 1; i++) {
>> -- 
>> 2.43.0
>>