On 2025/07/26 2:47, Viacheslav Dubeyko wrote:
>> I managed to find the offset of rec->dir.DirID in the filesystem image used by
>> the reproducer, and confirmed that any 0...15 values except 2..4 shall hit BUG()
>> in hfs_write_inode().
>>
>> Also, a legitimate filesystem image seems to have rec->dir.DirID == 2.
>>
>> That is, the only approach that can avoid hitting BUG() without removing BUG()
>> would be to verify that rec.type is HFS_CDR_DIR and rec.dir.DirID is HFS_ROOT_CNID.
>>
>> --- a/fs/hfs/super.c
>> +++ b/fs/hfs/super.c
>> @@ -354,7 +354,7 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
>> goto bail_hfs_find;
>> }
>> hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
>> - if (rec.type != HFS_CDR_DIR)
>> + if (rec.type != HFS_CDR_DIR || rec.dir.DirID != cpu_to_be32(HFS_ROOT_CNID))
>> res = -EIO;
>> }
>> if (res)
>>
>> Is this condition correct?
Please explicitly answer this question.
Is this validation correct that rec.dir.DirID has to be HFS_ROOT_CNID ?
res = hfs_cat_find_brec(sb, HFS_ROOT_CNID, &fd);
if (!res) {
if (fd.entrylength != sizeof(rec.dir)) {
res = -EIO;
goto bail_hfs_find;
}
hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
- if (rec.type != HFS_CDR_DIR)
+ if (rec.type != HFS_CDR_DIR || rec.dir.DirID != cpu_to_be32(HFS_ROOT_CNID))
res = -EIO;
}
I hope that this validation is correct because the "rec" which hfs_bnode_read()
reads is controlled by the result of hfs_cat_find_brec(HFS_ROOT_CNID).
>>
>> Discussion on what values should be filtered by hfs_read_inode() is
>> out of scope for this syzbot report.
>
> I already shared in previous emails which particular inode IDs are valid or not
> for [0-16] group of values in the environment of hfs_read_inode().
>
Checking which particular inode IDs hfs_read_inode() should accept is fine.
But such check cannot fix the bug reported at
https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b .
Checking the inode ID retrieved by hfs_cat_find_brec(HFS_ROOT_CNID) is indeed
HFS_ROOT_CNID can fix the bug reported at
https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b .
