parse_signed_commit: really use the entire commit log message

... even beyond the first NUL in the buffer, when checking the commit
against the detached signature in the header.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit.c

@@ -854,28 +854,31 @@ int parse_signed_commit(const unsigned char *sha1,
 	unsigned long size;
 	enum object_type type;
 	char *buffer = read_sha1_file(sha1, &type, &size);
-	int in_header, saw_signature = -1;
-	char *line;
+	int saw_signature = -1;
+	char *line, *tail;
 
 	if (!buffer || type != OBJ_COMMIT)
 		goto cleanup;
 
 	line = buffer;
-	in_header = 1;
+	tail = buffer + size;
 	saw_signature = 0;
-	while (*line) {
-		char *next = strchrnul(line, '\n');
-		if (*next)
+	while (line < tail) {
+		char *next = memchr(line, '\n', tail - line);
+		if (!next)
+			next = tail;
+		else
 			next++;
-		if (in_header && !prefixcmp(line, gpg_sig_header)) {
+		if (!prefixcmp(line, gpg_sig_header)) {
 			const char *sig = line + gpg_sig_header_len;
 			strbuf_add(signature, sig, next - sig);
 			saw_signature = 1;
 		} else {
+			if (*line == '\n')
+				/* dump the whole remainder of the buffer */
+				next = tail;
 			strbuf_add(payload, line, next - line);
 		}
-		if (*line == '\n')
-			in_header = 0;
 		line = next;
 	}
  cleanup:

t/t7510-signed-commit.sh

@@ -50,11 +50,22 @@ test_expect_success GPG 'show signatures' '
 
 test_expect_success GPG 'detect fudged signature' '
 	git cat-file commit master >raw &&
-	sed -e "s/fourth signed/4th forged/" raw >forged &&
-	git hash-object -w -t commit forged >forged.commit &&
-	git show --pretty=short --show-signature $(cat forged.commit) >actual &&
-	grep "BAD signature from" actual &&
-	! grep "Good signature from" actual
+
+	sed -e "s/fourth signed/4th forged/" raw >forged1 &&
+	git hash-object -w -t commit forged1 >forged1.commit &&
+	git show --pretty=short --show-signature $(cat forged1.commit) >actual1 &&
+	grep "BAD signature from" actual1 &&
+	! grep "Good signature from" actual1
+'
+
+test_expect_success GPG 'detect fudged signature with NUL' '
+	git cat-file commit master >raw &&
+	cat raw >forged2 &&
+	echo Qwik | tr "Q" "\000" >>forged2 &&
+	git hash-object -w -t commit forged2 >forged2.commit &&
+	git show --pretty=short --show-signature $(cat forged2.commit) >actual2 &&
+	grep "BAD signature from" actual2 &&
+	! grep "Good signature from" actual2
 '
 
 test_done