Fix a bug when getting a gzip header extra field with inflate().

Mark Adler · Mark Adler · commit eff308af425b · 2022-07-30T15:58:02.000-07:00
If the extra field was larger than the space the user provided with
inflateGetHeader(), and if multiple calls of inflate() delivered
the extra header data, then there could be a buffer overflow of the
provided space. This commit assures that provided space is not
exceeded.
diff --git a/inflate.c b/inflate.c
@@ -763,9 +763,10 @@ int flush;
                 copy = state->length;
                 if (copy > have) copy = have;
                 if (copy) {
+                    len = state->head->extra_len - state->length;
                     if (state->head != Z_NULL &&
-                        state->head->extra != Z_NULL) {
-                        len = state->head->extra_len - state->length;
+                        state->head->extra != Z_NULL &&
+                        len < state->head->extra_max) {
                         zmemcpy(state->head->extra + len, next,
                                 len + copy > state->head->extra_max ?
                                 state->head->extra_max - len : copy);
