Check *how many* fields sscanf() found.

In the code that parses a GeneralizedTime field, don't assume that all
fields were found; check the return value from sscanf().

This should clean up a fuzz failure on the 2.0 buildbot:

https://buildbot.wireshark.org/wireshark-2.0/builders/Fuzz%20Test/builds/13/steps/valgrind-wireshark/logs/stdio

Change-Id: I431d7ed69ac1697bd42c22a37ca1451cfc85c94e
Reviewed-on: https://code.wireshark.org/review/12083
Reviewed-by: Guy Harris <guy@alum.mit.edu>
(cherry picked from commit 921bb07115fbffc081ec56a5022b4a9d58db6d39)
Reviewed-on: https://code.wireshark.org/review/12085

1 files changed, 82 insertions, 31 deletions

diff --git a/epan/dissectors/packet-ber.c b/epan/dissectors/packet-ber.c
index ac8faf153c..fa47f9b934 100644
--- a/epan/dissectors/packet-ber.c
+++ b/epan/dissectors/packet-ber.c
@@ -3553,49 +3553,88 @@ dissect_ber_GeneralizedTime(gboolean implicit_tag, asn1_ctx_t *actx, proto_tree
     ret = sscanf( tmpstr, "%14d%1[.,+-Z]%4d%1[+-Z]%4d", &tmp_int, first_delim, &first_digits, second_delim, &second_digits);
     /* tmp_int does not contain valid value bacause of overflow but we use it just for format checking */
     if (ret < 1) {
-        cause = proto_tree_add_string_format_value(
-            tree, hf_ber_error, tvb, offset, len, "invalid_generalized_time",
-            "GeneralizedTime invalid format: %s",
-            tmpstr);
-        expert_add_info(actx->pinfo, cause, &ei_ber_invalid_format_generalized_time);
-        if (decode_unexpected) {
-            proto_tree *unknown_tree = proto_item_add_subtree(cause, ett_ber_unknown);
-            dissect_unknown_ber(actx->pinfo, tvb, offset, unknown_tree);
-        }
-        return end_offset;
+    	/* Nothing matched */
+        goto invalid;
     }
 
-    switch (first_delim[0]) {
-    case '.':
-    case ',':
-        strptr += g_snprintf(strptr, 5, "%c%.3d", first_delim[0], first_digits);
-        switch (second_delim[0]) {
+    if (ret >= 2) {
+        /*
+         * We saw the date+time and the first delimiter.
+         *
+         * Either:
+         *
+         *    it's '.' or ',', in which case we have a fraction of a
+         *    minute or hour;
+         *
+         *    it's '+' or '-', in which case we have an offset from UTC;
+         *
+         *    it's 'Z', in which case the time is UTC.
+         */
+        switch (first_delim[0]) {
+        case '.':
+        case ',':
+            /*
+             * Fraction of a minute or an hour.
+             */
+            if (ret == 2) {
+                /*
+                 * We saw the decimal sign, but didn't see the fraction.
+                 */
+                goto invalid;
+            }
+            strptr += g_snprintf(strptr, 5, "%c%.3d", first_delim[0], first_digits);
+            if (ret >= 4) {
+                /*
+                 * We saw the fraction and the second delimiter.
+                 *
+                 * Either:
+                 *
+                 *    it's '+' or '-', in which case we have an offset
+                 *    from UTC;
+                 *
+                 *    it's 'Z', in which case the time is UTC.
+                 */
+                switch (second_delim[0]) {
+                case '+':
+                case '-':
+                    if (ret == 4) {
+                        /*
+                         * We saw the + or -, but didn't see the offset
+                         * from UTC.
+                         */
+                        goto invalid;
+                    }
+                    g_snprintf(strptr, 12, " (UTC%c%.4d)", second_delim[0], second_digits);
+                    break;
+                case 'Z':
+                    g_snprintf(strptr, 7, " (UTC)");
+                    break;
+                default:
+                    /* handle the malformed field */
+                    break;
+                }
+            }
+            break;
         case '+':
         case '-':
-            g_snprintf(strptr, 12, " (UTC%c%.4d)", second_delim[0], second_digits);
+            /*
+             * Offset from UTC.
+             */
+            if (ret == 2) {
+                /*
+                 * We saw the + or -1, but didn't see the offset.
+                 */
+                goto invalid;
+            }
+            g_snprintf(strptr, 12, " (UTC%c%.4d)", first_delim[0], first_digits);
             break;
         case 'Z':
             g_snprintf(strptr, 7, " (UTC)");
             break;
-        case 0:
-            break;
         default:
             /* handle the malformed field */
             break;
         }
-        break;
-    case '+':
-    case '-':
-        g_snprintf(strptr, 12, " (UTC%c%.4d)", first_delim[0], first_digits);
-        break;
-    case 'Z':
-        g_snprintf(strptr, 7, " (UTC)");
-        break;
-    case 0:
-        break;
-    default:
-        /* handle the malformed field */
-        break;
     }
 
     if (hf_id >= 0) {
@@ -3604,6 +3643,18 @@ dissect_ber_GeneralizedTime(gboolean implicit_tag, asn1_ctx_t *actx, proto_tree
 
     offset+=len;
     return offset;
+
+invalid:
+    cause = proto_tree_add_string_format_value(
+        tree, hf_ber_error, tvb, offset, len, "invalid_generalized_time",
+        "GeneralizedTime invalid format: %s",
+        tmpstr);
+    expert_add_info(actx->pinfo, cause, &ei_ber_invalid_format_generalized_time);
+    if (decode_unexpected) {
+        proto_tree *unknown_tree = proto_item_add_subtree(cause, ett_ber_unknown);
+        dissect_unknown_ber(actx->pinfo, tvb, offset, unknown_tree);
+    }
+    return end_offset;
 }