setusercontext(): Better error messages when priority is not set corr…

…ectly

Polish the syslog messages to contain readily useful information.

Behavior of capability 'priority' is inconsistent with what is done for
all other contexts: 'umask', 'cpumask', resource limits, etc., where an
absence of capability means to inherit the value.  It is currently
preserved for compatibility, but is subject to change on a future major
release.

Reviewed by:            emaste, kib (older version)
Approved by:            emaste (mentor)
MFC after:              3 days
Sponsored by:           Kumacom SAS
Differential Revision:  https://reviews.freebsd.org/D40349

lib/libutil/login_class.c

@@ -473,9 +473,7 @@ setlogincontext(login_cap_t *lc, const struct passwd *pwd, unsigned long flags)
 int
 setusercontext(login_cap_t *lc, const struct passwd *pwd, uid_t uid, unsigned int flags)
 {
-    rlim_t	p;
     login_cap_t *llc = NULL;
-    struct rtprio rtp;
     int error;
 
     if (lc == NULL) {
@@ -492,30 +490,49 @@ setusercontext(login_cap_t *lc, const struct passwd *pwd, uid_t uid, unsigned in
 
     /* Set the process priority */
     if (flags & LOGIN_SETPRIORITY) {
-	p = login_getcapnum(lc, "priority", LOGIN_DEFPRI, LOGIN_DEFPRI);
+	const rlim_t def_val = LOGIN_DEFPRI, err_val = INT64_MIN;
+	rlim_t p = login_getcapnum(lc, "priority", def_val, err_val);
+	int rc;
+
+	if (p == err_val) {
+	    /* Invariant: 'lc' != NULL. */
+	    syslog(LOG_WARNING,
+		"%s%s%sLogin class '%s': "
+		"Invalid priority specification: '%s'",
+		pwd ? "Login '" : "",
+		pwd ? pwd->pw_name : "",
+		pwd ? "': " : "",
+		lc->lc_class,
+		login_getcapstr(lc, "priority", "", ""));
+	    /* Reset the priority, as if the capability was not present. */
+	    p = def_val;
+	}
 
 	if (p > PRIO_MAX) {
+	    struct rtprio rtp;
+
 	    rtp.type = RTP_PRIO_IDLE;
 	    p += RTP_PRIO_MIN - (PRIO_MAX + 1);
 	    rtp.prio = p > RTP_PRIO_MAX ? RTP_PRIO_MAX : p;
-	    if (rtprio(RTP_SET, 0, &rtp))
-		syslog(LOG_WARNING, "rtprio '%s' (%s): %m",
-		    pwd ? pwd->pw_name : "-",
-		    lc ? lc->lc_class : LOGIN_DEFCLASS);
+	    rc = rtprio(RTP_SET, 0, &rtp);
 	} else if (p < PRIO_MIN) {
+	    struct rtprio rtp;
+
 	    rtp.type = RTP_PRIO_REALTIME;
 	    p += RTP_PRIO_MAX - (PRIO_MIN - 1);
 	    rtp.prio = p < RTP_PRIO_MIN ? RTP_PRIO_MIN : p;
-	    if (rtprio(RTP_SET, 0, &rtp))
-		syslog(LOG_WARNING, "rtprio '%s' (%s): %m",
-		    pwd ? pwd->pw_name : "-",
-		    lc ? lc->lc_class : LOGIN_DEFCLASS);
-	} else {
-	    if (setpriority(PRIO_PROCESS, 0, (int)p) != 0)
-		syslog(LOG_WARNING, "setpriority '%s' (%s): %m",
-		    pwd ? pwd->pw_name : "-",
-		    lc ? lc->lc_class : LOGIN_DEFCLASS);
-	}
+	    rc = rtprio(RTP_SET, 0, &rtp);
+	} else
+	    rc = setpriority(PRIO_PROCESS, 0, (int)p);
+
+	if (rc != 0)
+	    syslog(LOG_WARNING,
+		"%s%s%sLogin class '%s': "
+		"Setting priority failed: %m",
+		pwd ? "Login '" : "",
+		pwd ? pwd->pw_name : "",
+		pwd ? "': " : "",
+		lc ? lc->lc_class : "<none>");
     }
 
     /* Setup the user's group permissions */