[PATCH 05/10] LSM: SafeSetID: refactor policy parsing

[Micah Morton]

Ready for merge.

On Wed, Apr 10, 2019 at 10:15 AM Kees Cook <keescook at chromium.org> wrote:
>
> On Wed, Apr 10, 2019 at 9:55 AM Micah Morton <mortonm at chromium.org> wrote:
> >
> > From: Jann Horn <jannh at google.com>
> >
> > In preparation for changing the policy parsing logic, refactor the line
> > parsing logic to be less verbose and move it into a separate function.
> >
> > Signed-off-by: Jann Horn <jannh at google.com>
> > Signed-off-by: Micah Morton <mortonm at chromium.org>
>
> Reviewed-by: Kees Cook <keescook at chromium.org>
>
> -Kees
>
> > ---
> > I made a minor change to Jann's original patch to use u32 instead of
> > s32 for the 'parsed_parent' and 'parsed_child' variables.
> >
> >  security/safesetid/securityfs.c | 84 +++++++++++++--------------------
> >  1 file changed, 33 insertions(+), 51 deletions(-)
> >
> > diff --git a/security/safesetid/securityfs.c b/security/safesetid/securityfs.c
> > index 2c6c829be044..90784a8d950a 100644
> > --- a/security/safesetid/securityfs.c
> > +++ b/security/safesetid/securityfs.c
> > @@ -33,68 +33,50 @@ static struct safesetid_file_entry safesetid_files[] = {
> >
> >  /*
> >   * In the case the input buffer contains one or more invalid UIDs, the kuid_t
> > - * variables pointed to by 'parent' and 'child' will get updated but this
> > + * variables pointed to by @parent and @child will get updated but this
> >   * function will return an error.
> > + * Contents of @buf may be modified.
> >   */
> > -static int parse_safesetid_whitelist_policy(const char __user *buf,
> > -                                           size_t len,
> > -                                           kuid_t *parent,
> > -                                           kuid_t *child)
> > +static int parse_policy_line(
> > +       struct file *file, char *buf, kuid_t *parent, kuid_t *child)
> >  {
> > -       char *kern_buf;
> > -       char *parent_buf;
> > -       char *child_buf;
> > -       const char separator[] = ":";
> > +       char *child_str;
> >         int ret;
> > -       size_t first_substring_length;
> > -       long parsed_parent;
> > -       long parsed_child;
> > +       u32 parsed_parent, parsed_child;
> >
> > -       /* Duplicate string from user memory and NULL-terminate */
> > -       kern_buf = memdup_user_nul(buf, len);
> > -       if (IS_ERR(kern_buf))
> > -               return PTR_ERR(kern_buf);
> > -
> > -       /*
> > -        * Format of |buf| string should be <UID>:<UID>.
> > -        * Find location of ":" in kern_buf (copied from |buf|).
> > -        */
> > -       first_substring_length = strcspn(kern_buf, separator);
> > -       if (first_substring_length == 0 || first_substring_length == len) {
> > -               ret = -EINVAL;
> > -               goto free_kern;
> > -       }
> > -
> > -       parent_buf = kmemdup_nul(kern_buf, first_substring_length, GFP_KERNEL);
> > -       if (!parent_buf) {
> > -               ret = -ENOMEM;
> > -               goto free_kern;
> > -       }
> > +       /* Format of |buf| string should be <UID>:<UID>. */
> > +       child_str = strchr(buf, ':');
> > +       if (child_str == NULL)
> > +               return -EINVAL;
> > +       *child_str = '\0';
> > +       child_str++;
> >
> > -       ret = kstrtol(parent_buf, 0, &parsed_parent);
> > +       ret = kstrtou32(buf, 0, &parsed_parent);
> >         if (ret)
> > -               goto free_both;
> > +               return ret;
> >
> > -       child_buf = kern_buf + first_substring_length + 1;
> > -       ret = kstrtol(child_buf, 0, &parsed_child);
> > +       ret = kstrtou32(child_str, 0, &parsed_child);
> >         if (ret)
> > -               goto free_both;
> > +               return ret;
> >
> >         *parent = make_kuid(current_user_ns(), parsed_parent);
> > -       if (!uid_valid(*parent)) {
> > -               ret = -EINVAL;
> > -               goto free_both;
> > -       }
> > -
> >         *child = make_kuid(current_user_ns(), parsed_child);
> > -       if (!uid_valid(*child)) {
> > -               ret = -EINVAL;
> > -               goto free_both;
> > -       }
> > +       if (!uid_valid(*parent) || !uid_valid(*child))
> > +               return -EINVAL;
> >
> > -free_both:
> > -       kfree(parent_buf);
> > -free_kern:
> > +       return 0;
> > +}
> > +
> > +static int parse_safesetid_whitelist_policy(
> > +       struct file *file, const char __user *buf, size_t len,
> > +       kuid_t *parent, kuid_t *child)
> > +{
> > +       char *kern_buf = memdup_user_nul(buf, len);
> > +       int ret;
> > +
> > +       if (IS_ERR(kern_buf))
> > +               return PTR_ERR(kern_buf);
> > +       ret = parse_policy_line(file, kern_buf, parent, child);
> >         kfree(kern_buf);
> >         return ret;
> >  }
> > @@ -121,8 +103,8 @@ static ssize_t safesetid_file_write(struct file *file,
> >                 flush_safesetid_whitelist_entries();
> >                 break;
> >         case SAFESETID_WHITELIST_ADD:
> > -               ret = parse_safesetid_whitelist_policy(buf, len, &parent,
> > -                                                                &child);
> > +               ret = parse_safesetid_whitelist_policy(file, buf, len,
> > +                                                      &parent, &child);
> >                 if (ret)
> >                         return ret;
> >
> > --
> > 2.21.0.392.gf8f6787159e-goog
> >
>
>
> --
> Kees Cook