[PATCH] CIFS: Fix a potencially linear read overflow

[Steve French]

Added RB and repushed to cifs-2.6.git for-next

On Wed, Aug 18, 2021 at 8:22 AM Jeff Layton <jlayton at kernel.org> wrote:
>
> On Tue, 2021-08-17 at 12:27 +0200, Len Baker wrote:
> > strlcpy() reads the entire source buffer first. This read may exceed the
> > destination size limit. This is both inefficient and can lead to linear
> > read overflows if a source string is not NUL-terminated.
> >
> > Also, the strnlen() call does not avoid the read overflow in the strlcpy
> > function when a not NUL-terminated string is passed.
> >
> > So, replace this block by a call to kstrndup() that avoids this type of
> > overflow and does the same.
> >
> > Fixes: 066ce6899484d ("cifs: rename cifs_strlcpy_to_host and make it use new functions")
> > Signed-off-by: Len Baker <len.baker at gmx.com>
> > ---
> >  fs/cifs/cifs_unicode.c | 9 ++-------
> >  1 file changed, 2 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/cifs/cifs_unicode.c b/fs/cifs/cifs_unicode.c
> > index 9bd03a231032..171ad8b42107 100644
> > --- a/fs/cifs/cifs_unicode.c
> > +++ b/fs/cifs/cifs_unicode.c
> > @@ -358,14 +358,9 @@ cifs_strndup_from_utf16(const char *src, const int maxlen,
> >               if (!dst)
> >                       return NULL;
> >               cifs_from_utf16(dst, (__le16 *) src, len, maxlen, codepage,
> > -                            NO_MAP_UNI_RSVD);
> > +                             NO_MAP_UNI_RSVD);
> >       } else {
> > -             len = strnlen(src, maxlen);
> > -             len++;
> > -             dst = kmalloc(len, GFP_KERNEL);
> > -             if (!dst)
> > -                     return NULL;
> > -             strlcpy(dst, src, len);
> > +             dst = kstrndup(src, maxlen, GFP_KERNEL);
> >       }
> >
> >       return dst;
> > --
> > 2.25.1
> >
>
> Reviewed-by: Jeff Layton <jlayton at kernel.org>
>


-- 
Thanks,

Steve