check_snmp: Fix support for inverse thresholds

Commit bd782990566eec91b8312cfc2765a7e2bd9e67da reintroduced support for
inverse threshold ranges such as "2:1", but it broke standard thresholds
such as "1:2" (by converting this range into "1") or "1:" (by converting
this range into "@:2").  This commit fixes those two bugs, plus an
off-by-one error while computing the number of bytes to allocate when
handling inverse thresholds (two additional bytes were allocated where
three were required to hold '@' and ':' and '\0').  While at it, we also
check whether malloc(3) succeeded.

1 files changed, 7 insertions, 5 deletions

diff --git a/plugins/check_snmp.c b/plugins/check_snmp.c
index 7c3bc4b9..d2f2f8b5 100644
--- a/plugins/check_snmp.c
+++ b/plugins/check_snmp.c
@@ -150,16 +150,18 @@ static char *fix_snmp_range(char *th)
 {
         double left, right;
         char *colon, *ret;
-        if (!(colon = strchr(th, ':')))
+
+        if ((colon = strchr(th, ':')) == NULL || *(colon + 1) == '\0')
                 return th;
-        *colon = 0;
 
         left = strtod(th, NULL);
         right = strtod(colon + 1, NULL);
-        if (right >= left) {
+        if (right >= left)
                 return th;
-        }
-        ret = malloc(strlen(th) + strlen(colon + 1) + 2);
+
+        if ((ret = malloc(strlen(th) + 2)) == NULL)
+                die(STATE_UNKNOWN, _("Cannot malloc"));
+        *colon = '\0';
         sprintf(ret, "@%s:%s", colon + 1, th);
         free(th);
         return ret;