lzw: Reject bad LZW Minimum Code Size.

The libnsgif.c code was checking this incorrectly, so safest to
check it in the lzw.c code.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/lzw.c b/src/lzw.c
index 50d1d22..1f85496 100644
--- a/src/lzw.c
+++ b/src/lzw.c
@@ -272,6 +272,10 @@ lzw_result lzw_decode_init(
 {
 	struct lzw_dictionary_entry *table = ctx->table;
 
+	if (code_size >= LZW_CODE_MAX) {
+		return LZW_BAD_ICODE;
+	}
+
 	/* Initialise the input reading context */
 	ctx->input.data = compressed_data;
 	ctx->input.data_len = compressed_data_len;