[V4,01/10] capabilities: factor out cap_bprm_set_creds privileged root
diff mbox

Message ID c9900dda93bac311a7ce7da753eb430905301276.1504591358.git.rgb@redhat.com
State New
Headers show

Commit Message

Richard Guy Briggs Sept. 5, 2017, 6:46 a.m. UTC
Factor out the case of privileged root from the function
cap_bprm_set_creds() to make the latter easier to read and analyse.

Suggested-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
---
 security/commoncap.c |   63 +++++++++++++++++++++++++++----------------------
 1 files changed, 35 insertions(+), 28 deletions(-)

Comments

James Morris Sept. 6, 2017, 6:05 a.m. UTC | #1
On Tue, 5 Sep 2017, Richard Guy Briggs wrote:

> Factor out the case of privileged root from the function
> cap_bprm_set_creds() to make the latter easier to read and analyse.
> 
> Suggested-by: Serge Hallyn <serge@hallyn.com>
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
> ---
>  security/commoncap.c |   63 +++++++++++++++++++++++++++----------------------
>  1 files changed, 35 insertions(+), 28 deletions(-)


Acked-by: James Morris <james.l.morris@oracle.com>
Kees Cook Sept. 7, 2017, 7:42 p.m. UTC | #2
On Mon, Sep 4, 2017 at 11:46 PM, Richard Guy Briggs <rgb@redhat.com> wrote:
> Factor out the case of privileged root from the function
> cap_bprm_set_creds() to make the latter easier to read and analyse.
>
> Suggested-by: Serge Hallyn <serge@hallyn.com>
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>

Acked-by: Kees Cook <keescook@chromium.org>

Note below...

> ---
>  security/commoncap.c |   63 +++++++++++++++++++++++++++----------------------
>  1 files changed, 35 insertions(+), 28 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index d8e26fb..927fe93 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -472,6 +472,39 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
>         return rc;
>  }
>
> +static void handle_privileged_root(struct linux_binprm *bprm, bool has_cap,
> +                                  bool *effective, kuid_t root_uid)

If you do a v5 of this, I think it'd be nice to add a comment here
describing what is being checked and the side-effects (i.e.
cap_permitted changes, when effective is set, etc).

-Kees

> +{
> +       const struct cred *old = current_cred();
> +       struct cred *new = bprm->cred;
> +
> +       if (issecure(SECURE_NOROOT))
> +               return;
> +       /*
> +        * If the legacy file capability is set, then don't set privs
> +        * for a setuid root binary run by a non-root user.  Do set it
> +        * for a root user just to cause least surprise to an admin.
> +        */
> +       if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
> +               warn_setuid_and_fcaps_mixed(bprm->filename);
> +               return;
> +       }
> +       /*
> +        * To support inheritance of root-permissions and suid-root
> +        * executables under compatibility mode, we override the
> +        * capability sets for the file.
> +        *
> +        * If only the real uid is 0, we do not set the effective bit.
> +        */
> +       if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
> +               /* pP' = (cap_bset & ~0) | (pI & ~0) */
> +               new->cap_permitted = cap_combine(old->cap_bset,
> +                                                old->cap_inheritable);
> +       }
> +       if (uid_eq(new->euid, root_uid))
> +               *effective = true;
> +}
> +
>  /**
>   * cap_bprm_set_creds - Set up the proposed credentials for execve().
>   * @bprm: The execution parameters, including the proposed creds
> @@ -484,46 +517,20 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
>  {
>         const struct cred *old = current_cred();
>         struct cred *new = bprm->cred;
> -       bool effective, has_cap = false, is_setid;
> +       bool effective = false, has_cap = false, is_setid;
>         int ret;
>         kuid_t root_uid;
>
>         if (WARN_ON(!cap_ambient_invariant_ok(old)))
>                 return -EPERM;
>
> -       effective = false;
>         ret = get_file_caps(bprm, &effective, &has_cap);
>         if (ret < 0)
>                 return ret;
>
>         root_uid = make_kuid(new->user_ns, 0);
>
> -       if (!issecure(SECURE_NOROOT)) {
> -               /*
> -                * If the legacy file capability is set, then don't set privs
> -                * for a setuid root binary run by a non-root user.  Do set it
> -                * for a root user just to cause least surprise to an admin.
> -                */
> -               if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
> -                       warn_setuid_and_fcaps_mixed(bprm->filename);
> -                       goto skip;
> -               }
> -               /*
> -                * To support inheritance of root-permissions and suid-root
> -                * executables under compatibility mode, we override the
> -                * capability sets for the file.
> -                *
> -                * If only the real uid is 0, we do not set the effective bit.
> -                */
> -               if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
> -                       /* pP' = (cap_bset & ~0) | (pI & ~0) */
> -                       new->cap_permitted = cap_combine(old->cap_bset,
> -                                                        old->cap_inheritable);
> -               }
> -               if (uid_eq(new->euid, root_uid))
> -                       effective = true;
> -       }
> -skip:
> +       handle_privileged_root(bprm, has_cap, &effective, root_uid);
>
>         /* if we have fs caps, clear dangerous personality flags */
>         if (!cap_issubset(new->cap_permitted, old->cap_permitted))
> --
> 1.7.1
>

Patch
diff mbox

diff --git a/security/commoncap.c b/security/commoncap.c
index d8e26fb..927fe93 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -472,6 +472,39 @@  static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
 	return rc;
 }
 
+static void handle_privileged_root(struct linux_binprm *bprm, bool has_cap,
+				   bool *effective, kuid_t root_uid)
+{
+	const struct cred *old = current_cred();
+	struct cred *new = bprm->cred;
+
+	if (issecure(SECURE_NOROOT))
+		return;
+	/*
+	 * If the legacy file capability is set, then don't set privs
+	 * for a setuid root binary run by a non-root user.  Do set it
+	 * for a root user just to cause least surprise to an admin.
+	 */
+	if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
+		warn_setuid_and_fcaps_mixed(bprm->filename);
+		return;
+	}
+	/*
+	 * To support inheritance of root-permissions and suid-root
+	 * executables under compatibility mode, we override the
+	 * capability sets for the file.
+	 *
+	 * If only the real uid is 0, we do not set the effective bit.
+	 */
+	if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
+		/* pP' = (cap_bset & ~0) | (pI & ~0) */
+		new->cap_permitted = cap_combine(old->cap_bset,
+						 old->cap_inheritable);
+	}
+	if (uid_eq(new->euid, root_uid))
+		*effective = true;
+}
+
 /**
  * cap_bprm_set_creds - Set up the proposed credentials for execve().
  * @bprm: The execution parameters, including the proposed creds
@@ -484,46 +517,20 @@  int cap_bprm_set_creds(struct linux_binprm *bprm)
 {
 	const struct cred *old = current_cred();
 	struct cred *new = bprm->cred;
-	bool effective, has_cap = false, is_setid;
+	bool effective = false, has_cap = false, is_setid;
 	int ret;
 	kuid_t root_uid;
 
 	if (WARN_ON(!cap_ambient_invariant_ok(old)))
 		return -EPERM;
 
-	effective = false;
 	ret = get_file_caps(bprm, &effective, &has_cap);
 	if (ret < 0)
 		return ret;
 
 	root_uid = make_kuid(new->user_ns, 0);
 
-	if (!issecure(SECURE_NOROOT)) {
-		/*
-		 * If the legacy file capability is set, then don't set privs
-		 * for a setuid root binary run by a non-root user.  Do set it
-		 * for a root user just to cause least surprise to an admin.
-		 */
-		if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
-			warn_setuid_and_fcaps_mixed(bprm->filename);
-			goto skip;
-		}
-		/*
-		 * To support inheritance of root-permissions and suid-root
-		 * executables under compatibility mode, we override the
-		 * capability sets for the file.
-		 *
-		 * If only the real uid is 0, we do not set the effective bit.
-		 */
-		if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
-			/* pP' = (cap_bset & ~0) | (pI & ~0) */
-			new->cap_permitted = cap_combine(old->cap_bset,
-							 old->cap_inheritable);
-		}
-		if (uid_eq(new->euid, root_uid))
-			effective = true;
-	}
-skip:
+	handle_privileged_root(bprm, has_cap, &effective, root_uid);
 
 	/* if we have fs caps, clear dangerous personality flags */
 	if (!cap_issubset(new->cap_permitted, old->cap_permitted))