1 files changed, 47 insertions, 12 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b0e940497e23..6c90d491fab4 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2097,6 +2097,41 @@ static int selinux_vm_enough_memory(struct mm_struct *mm, long pages)
 
 /* binprm security operations */
 
+static int check_nnp_nosuid(const struct linux_binprm *bprm,
+			    const struct task_security_struct *old_tsec,
+			    const struct task_security_struct *new_tsec)
+{
+	int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS);
+	int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID);
+	int rc;
+
+	if (!nnp && !nosuid)
+		return 0; /* neither NNP nor nosuid */
+
+	if (new_tsec->sid == old_tsec->sid)
+		return 0; /* No change in credentials */
+
+	/*
+	 * The only transitions we permit under NNP or nosuid
+	 * are transitions to bounded SIDs, i.e. SIDs that are
+	 * guaranteed to only be allowed a subset of the permissions
+	 * of the current SID.
+	 */
+	rc = security_bounded_transition(old_tsec->sid, new_tsec->sid);
+	if (rc) {
+		/*
+		 * On failure, preserve the errno values for NNP vs nosuid.
+		 * NNP:  Operation not permitted for caller.
+		 * nosuid:  Permission denied to file.
+		 */
+		if (nnp)
+			return -EPERM;
+		else
+			return -EACCES;
+	}
+	return 0;
+}
+
 static int selinux_bprm_set_creds(struct linux_binprm *bprm)
 {
 	const struct task_security_struct *old_tsec;
@@ -2133,14 +2168,10 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
 		/* Reset exec SID on execve. */
 		new_tsec->exec_sid = 0;
 
-		/*
-		 * Minimize confusion: if no_new_privs or nosuid and a
-		 * transition is explicitly requested, then fail the exec.
-		 */
-		if (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS)
-			return -EPERM;
-		if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
-			return -EACCES;
+		/* Fail on NNP or nosuid if not an allowed transition. */
+		rc = check_nnp_nosuid(bprm, old_tsec, new_tsec);
+		if (rc)
+			return rc;
 	} else {
 		/* Check for a default transition on this program. */
 		rc = security_transition_sid(old_tsec->sid, isec->sid,
@@ -2148,15 +2179,19 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
 					     &new_tsec->sid);
 		if (rc)
 			return rc;
+
+		/*
+		 * Fallback to old SID on NNP or nosuid if not an allowed
+		 * transition.
+		 */
+		rc = check_nnp_nosuid(bprm, old_tsec, new_tsec);
+		if (rc)
+			new_tsec->sid = old_tsec->sid;
 	}
 
 	ad.type = LSM_AUDIT_DATA_PATH;
 	ad.u.path = bprm->file->f_path;
 
-	if ((bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) ||
-	    (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS))
-		new_tsec->sid = old_tsec->sid;
-
 	if (new_tsec->sid == old_tsec->sid) {
 		rc = avc_has_perm(old_tsec->sid, isec->sid,
 				  SECCLASS_FILE, FILE__EXECUTE_NO_TRANS, &ad);