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

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.

1 files changed, 3 insertions, 2 deletions

diff --git a/inflate.c b/inflate.c
index 7be8c63..7a72897 100644
--- 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);