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SubjectRe: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup
On Tue, Dec 10, 2019 at 11:19:13AM -0800, Eric Biggers wrote:
> > +static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
> > +{
> > + if (unlikely(name[0] == '.')) {
> > + if (len < 2 || (len == 2 && name[1] == '.'))
> > + return true;
> > + }
> > +
> > + return false;
> > +}
>
> This doesn't handle the len=0 case. Did you check that none of the users pass
> in zero-length names? It looks like fscrypt_fname_disk_to_usr() can, if the
> directory entry on-disk has a zero-length name. Currently it will return
> -EUCLEAN in that case, but with this patch it may think it's the name ".".

Trying to wrench this back on track ...

fscrypt_fname_disk_to_usr is called by:

fscrypt_get_symlink():
if (cstr.len == 0)
return ERR_PTR(-EUCLEAN);
ext4_readdir():
Does not currently check de->name_len. I believe this check should
be added to __ext4_check_dir_entry() because a zero-length directory
entry can affect both encrypted and non-encrypted directory entries.
dx_show_leaf():
Same as ext4_readdir(). Should probably call ext4_check_dir_entry()?
htree_dirblock_to_tree():
Would be covered by a fix to ext4_check_dir_entry().
f2fs_fill_dentries():
if (de->name_len == 0) {
...
ubifs_readdir():
Does not currently check de->name_len. Also affects non-encrypted
directory entries.

So of the six callers, two of them already check the dirent length for
being zero, and four of them ought to anyway, but don't. I think they
should be fixed, but clearly we don't historically check for this kind
of data corruption (strangely), so I don't think that's a reason to hold
up this patch until the individual filesystems are fixed.

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