fix crashes identified by sentry (#19856)

* check for the existance of rc->rrdset

* avoid division by zero

* format rfc3339 days avoiding sprintf

src/collectors/cgroups.plugin/cgroup-charts.c

@@ -449,7 +449,7 @@ void update_mem_pgfaults_chart(struct cgroup *cg) {
 }
 
 void update_mem_usage_limit_chart(struct cgroup *cg, unsigned long long memory_limit) {
-    if (is_cgroup_systemd_service(cg))
+    if (is_cgroup_systemd_service(cg) || !memory_limit)
         return;
 
     RRDSET *chart = cg->st_mem_usage_limit;
@@ -488,7 +488,7 @@ void update_mem_usage_limit_chart(struct cgroup *cg, unsigned long long memory_l
 }
 
 void update_mem_utilization_chart(struct cgroup *cg, unsigned long long memory_limit) {
-    if (is_cgroup_systemd_service(cg))
+    if (is_cgroup_systemd_service(cg) || !memory_limit)
         return;
 
     RRDSET *chart = cg->st_mem_utilization;

src/health/health_variable.c

@@ -36,7 +36,7 @@ struct variable_lookup_job {
 };
 
 static void variable_lookup_add_result_with_score(struct variable_lookup_job *vbd, NETDATA_DOUBLE n, RRDSET *st, const char *source __maybe_unused) {
-    if(vbd->score.last_rrdset != st) {
+    if(vbd->score.last_rrdset != st && vbd->rc->rrdset) {
         vbd->score.last_rrdset = st;
         vbd->score.last_score = rrdlabels_common_count(vbd->rc->rrdset->rrdlabels, st->rrdlabels);
     }

src/libnetdata/datetime/rfc3339.c

@@ -4,8 +4,71 @@
 
 #include "rfc3339.h"
 
+// Helper functions for safe printing of date/time components
+// These functions don't add a null terminator and return only the exact count of bytes written
+
+static inline size_t print_4digit_year(char *buffer, size_t size, int year) {
+    if (!buffer || size < 4) return 0; // Need at least 4 digits
+
+    // Ensure year is in valid range (0-9999)
+    year = year < 0 ? 0 : (year > 9999 ? 9999 : year);
+
+    buffer[0] = '0' + (year / 1000) % 10;
+    buffer[1] = '0' + (year / 100) % 10;
+    buffer[2] = '0' + (year / 10) % 10;
+    buffer[3] = '0' + year % 10;
+
+    return 4;
+}
+
+static inline size_t print_2digit(char *buffer, size_t size, int value) {
+    if (!buffer || size < 2) return 0; // Need at least 2 digits
+
+    // Ensure value is in valid range (0-99)
+    value = value < 0 ? 0 : (value > 99 ? 99 : value);
+
+    buffer[0] = '0' + (value / 10) % 10;
+    buffer[1] = '0' + value % 10;
+
+    return 2;
+}
+
+static inline size_t print_fraction(char *buffer, size_t size, usec_t fraction, size_t digits) {
+    if (!buffer || size < digits) return 0;
+
+    // Validate and cap the number of digits
+    digits = digits < 1 ? 1 : (digits > 9 ? 9 : digits);
+
+    // Calculate divisor to get correct precision
+    usec_t divisor = 1;
+    for (size_t i = 0; i < 6 - digits; i++)
+        divisor *= 10;
+
+    // Calculate the fraction to print
+    fraction = fraction / divisor;
+
+    // Ensure fraction won't exceed the requested number of digits
+    usec_t max_value = 1;
+    for (size_t i = 0; i < digits; i++)
+        max_value *= 10;
+    max_value--;
+
+    fraction = fraction > max_value ? max_value : fraction;
+
+    // Print the fraction with leading zeros
+    usec_t remaining = fraction;
+
+    // Setup working backwards from least significant digit
+    for (int i = digits - 1; i >= 0; i--) {
+        buffer[i] = '0' + (remaining % 10);
+        remaining /= 10;
+    }
+
+    return digits;
+}
+
 size_t rfc3339_datetime_ut(char *buffer, size_t len, usec_t now_ut, size_t fractional_digits, bool utc) {
-    if (!buffer || len == 0)
+    if (!buffer || len < 20) // Minimum size for YYYY-MM-DDThh:mm:ssZ
         return 0;
 
     time_t t = (time_t)(now_ut / USEC_PER_SEC);
@@ -21,43 +84,108 @@ size_t rfc3339_datetime_ut(char *buffer, size_t len, usec_t now_ut, size_t fract
         return 0;
     }
 
-    size_t used_length = strftime(buffer, len, "%Y-%m-%dT%H:%M:%S", tmp);
+    size_t pos = 0;
-    if (used_length == 0) {
-        buffer[0] = '\0';
-        return 0;
-    }
 
-    if (fractional_digits >= 1 && fractional_digits <= 9) {
+    // Year (4 digits)
-        int fractional_part = (int)(now_ut % USEC_PER_SEC);
+    if (len - pos < 4) goto finish;
-        if (fractional_part && len - used_length > fractional_digits + 1) {
+    pos += print_4digit_year(&buffer[pos], len - pos, tmp->tm_year + 1900);
-            char format[] = ".%01d";
-            format[3] = (char)('0' + fractional_digits);
 
-            // Adjust fractional part
+    // Month separator
-            fractional_part /= (int)pow(10, 6 - fractional_digits);
+    if (len - pos < 1) goto finish;
+    buffer[pos++] = '-';
 
-            used_length += snprintf(buffer + used_length, len - used_length,
+    // Month (2 digits)
-                                    format, fractional_part);
+    if (len - pos < 2) goto finish;
+    pos += print_2digit(&buffer[pos], len - pos, tmp->tm_mon + 1);
+
+    // Day separator
+    if (len - pos < 1) goto finish;
+    buffer[pos++] = '-';
+
+    // Day (2 digits)
+    if (len - pos < 2) goto finish;
+    pos += print_2digit(&buffer[pos], len - pos, tmp->tm_mday);
+
+    // T separator
+    if (len - pos < 1) goto finish;
+    buffer[pos++] = 'T';
+
+    // Hour (2 digits)
+    if (len - pos < 2) goto finish;
+    pos += print_2digit(&buffer[pos], len - pos, tmp->tm_hour);
+
+    // Minute separator
+    if (len - pos < 1) goto finish;
+    buffer[pos++] = ':';
+
+    // Minute (2 digits)
+    if (len - pos < 2) goto finish;
+    pos += print_2digit(&buffer[pos], len - pos, tmp->tm_min);
+
+    // Second separator
+    if (len - pos < 1) goto finish;
+    buffer[pos++] = ':';
+
+    // Second (2 digits)
+    if (len - pos < 2) goto finish;
+    pos += print_2digit(&buffer[pos], len - pos, tmp->tm_sec);
+
+    // Add fractional part if requested
+    if (fractional_digits > 9) fractional_digits = 9;
+    if (fractional_digits) {
+        usec_t fractional_part = now_ut % USEC_PER_SEC;
+
+        if (fractional_part > 0) {
+            // Need space for decimal point and digits
+            if (len - pos < fractional_digits + 1) goto finish;
+
+            buffer[pos++] = '.';
+            pos += print_fraction(&buffer[pos], len - pos, fractional_part, fractional_digits);
         }
     }
 
+    // Add timezone information
     if (utc) {
-        if (used_length + 1 < len) {
+        if (len - pos < 1) goto finish;
-            buffer[used_length++] = 'Z';
+        buffer[pos++] = 'Z';
-            buffer[used_length] = '\0';
-        }
     }
     else {
         long offset = tmbuf.tm_gmtoff;
         int hours = (int)(offset / 3600);
         int minutes = abs((int)((offset % 3600) / 60));
 
-        if (used_length + 7 < len) { // Space for "+HH:MM\0"
+        // Check if timezone is UTC
-            used_length += snprintf(buffer + used_length, len - used_length, "%+03d:%02d", hours, minutes);
+        if (hours == 0 && minutes == 0) {
+            if (len - pos < 1) goto finish;
+            buffer[pos++] = 'Z';
+        }
+        else {
+            // Need space for sign, hours, colon, minutes (6 chars total)
+            if (len - pos < 6) goto finish;
+
+            // Add timezone offset
+            buffer[pos++] = (hours >= 0) ? '+' : '-';
+            hours = abs(hours);
+
+            // Hours with leading zero
+            pos += print_2digit(&buffer[pos], len - pos, hours);
+
+            // Colon
+            buffer[pos++] = ':';
+
+            // Minutes with leading zero
+            pos += print_2digit(&buffer[pos], len - pos, minutes);
         }
     }
 
-    return used_length;
+finish:
+    // Ensure null termination
+    if (pos < len)
+        buffer[pos] = '\0';
+    else
+        buffer[len - 1] = '\0';
+
+    return pos;
 }
 
 usec_t rfc3339_parse_ut(const char *rfc3339, char **endptr) {