Re: [PATCH v4] fs: introduce is_dot_or_dotdot helper for cleanup

[Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>]

On 12/11/2019 03:19 AM, Eric Biggers wrote:
> On Tue, Dec 10, 2019 at 08:10:01PM +0800, Tiezhu Yang wrote:
> > diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
> > index 3da3707..ef7eba8 100644
> > --- a/fs/crypto/fname.c
> > +++ b/fs/crypto/fname.c
> > @@ -11,21 +11,11 @@
> >    * This has not yet undergone a rigorous security audit.
> >    */
> >   
> > +#include <linux/namei.h>
> >   #include <linux/scatterlist.h>
> >   #include <crypto/skcipher.h>
> >   #include "fscrypt_private.h"
> >   
> > -static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
> > -{
> > -	if (str->len == 1 && str->name[0] == '.')
> > -		return true;
> > -
> > -	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
> > -		return true;
> > -
> > -	return false;
> > -}
> > -
> >   /**
> >    * fname_encrypt() - encrypt a filename
> >    *
> > @@ -255,7 +245,7 @@ int fscrypt_fname_disk_to_usr(struct inode *inode,
> >   	const struct qstr qname = FSTR_TO_QSTR(iname);
> >   	struct fscrypt_digested_name digested_name;
> >   
> > -	if (fscrypt_is_dot_dotdot(&qname)) {
> > +	if (is_dot_or_dotdot(qname.name, qname.len)) {
> There's no need for the 'qname' variable anymore.  Can you please remove it and
> do:
>
> 	if (is_dot_or_dotdot(iname->name, iname->len)) {

Hi Eric,

Thanks for your review, I will do it in the v5 patch.

> > diff --git a/include/linux/namei.h b/include/linux/namei.h
> > index 7fe7b87..aba114a 100644
> > --- a/include/linux/namei.h
> > +++ b/include/linux/namei.h
> > @@ -92,4 +92,14 @@ retry_estale(const long error, const unsigned int flags)
> >   	return error == -ESTALE && !(flags & LOOKUP_REVAL);
> >   }
> >   
> > +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 ".".
>
> So I think there needs to either be a len >= 1 check added, *or* you need to
> make an argument for why it's okay to not care about the empty name case.

Anyway, let me modify the if condition "len < 2" to "len == 1".

static inline bool is_dot_or_dotdot(const unsigned char *name, size_t len)
{
        if (unlikely(name[0] == '.')) {
                if (len == 1 || (len == 2 && name[1] == '.'))
                        return true;
        }

        return false;
}

I will send v5 patch as soon as possible.

Thanks,

Tiezhu Yang

> - Eric