commit --amend -S: strip existing gpgsig headers

gitster · gitster · commit c871a1d17b84 · 2012-01-05T13:02:26.000-08:00
Any existing commit signature was made against the contents of the old
commit, including its committer date that is about to change, and will
become invalid by amending it.

Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/builtin/commit.c b/builtin/commit.c
@@ -1494,7 +1494,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	}
 
 	if (amend) {
-		extra = read_commit_extra_headers(current_head);
+		const char *exclude_gpgsig[2] = { "gpgsig", NULL };
+		extra = read_commit_extra_headers(current_head, exclude_gpgsig);
 	} else {
 		struct commit_extra_header **tail = &extra;
 		append_merge_tag_headers(parents, &tail);
diff --git a/commit.c b/commit.c
@@ -981,14 +981,15 @@ static void add_extra_header(struct strbuf *buffer,
 		strbuf_addch(buffer, '\n');
 }
 
-struct commit_extra_header *read_commit_extra_headers(struct commit *commit)
+struct commit_extra_header *read_commit_extra_headers(struct commit *commit,
+						      const char **exclude)
 {
 	struct commit_extra_header *extra = NULL;
 	unsigned long size;
 	enum object_type type;
 	char *buffer = read_sha1_file(commit->object.sha1, &type, &size);
 	if (buffer && type == OBJ_COMMIT)
-		extra = read_commit_extra_header_lines(buffer, size);
+		extra = read_commit_extra_header_lines(buffer, size, exclude);
 	free(buffer);
 	return extra;
 }
@@ -1002,7 +1003,23 @@ static inline int standard_header_field(const char *field, size_t len)
 		(len == 8 && !memcmp(field, "encoding ", 9)));
 }
 
-struct commit_extra_header *read_commit_extra_header_lines(const char *buffer, size_t size)
+static int excluded_header_field(const char *field, size_t len, const char **exclude)
+{
+	if (!exclude)
+		return 0;
+
+	while (*exclude) {
+		size_t xlen = strlen(*exclude);
+		if (len == xlen &&
+		    !memcmp(field, *exclude, xlen) && field[xlen] == ' ')
+			return 1;
+		exclude++;
+	}
+	return 0;
+}
+
+struct commit_extra_header *read_commit_extra_header_lines(const char *buffer, size_t size,
+							   const char **exclude)
 {
 	struct commit_extra_header *extra = NULL, **tail = &extra, *it = NULL;
 	const char *line, *next, *eof, *eob;
@@ -1028,7 +1045,8 @@ struct commit_extra_header *read_commit_extra_header_lines(const char *buffer, s
 		if (next <= eof)
 			eof = next;
 
-		if (standard_header_field(line, eof - line))
+		if (standard_header_field(line, eof - line) ||
+		    excluded_header_field(line, eof - line, exclude))
 			continue;
 
 		it = xcalloc(1, sizeof(*it));
diff --git a/commit.h b/commit.h
@@ -200,8 +200,8 @@ extern int commit_tree_extended(const char *msg, unsigned char *tree,
 				const char *author, const char *sign_commit,
 				struct commit_extra_header *);
 
-extern struct commit_extra_header *read_commit_extra_headers(struct commit *);
-extern struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len);
+extern struct commit_extra_header *read_commit_extra_headers(struct commit *, const char **);
+extern struct commit_extra_header *read_commit_extra_header_lines(const char *buf, size_t len, const char **);
 
 extern void free_commit_extra_headers(struct commit_extra_header *extra);
 
diff --git a/t/t7510-signed-commit.sh b/t/t7510-signed-commit.sh
@@ -24,7 +24,8 @@ test_expect_success GPG 'create signed commits' '
 	echo 4 >file && test_tick && git commit -a -m "fourth unsigned" &&
 	git tag fourth-unsigned &&
 
-	test_tick && git commit --amend -S -m "fourth signed"
+	test_tick && git commit --amend -S -m "fourth signed" &&
+	git tag fourth-signed
 '
 
 test_expect_success GPG 'show signatures' '
@@ -68,4 +69,12 @@ test_expect_success GPG 'detect fudged signature with NUL' '
 	! grep "Good signature from" actual2
 '
 
+test_expect_success GPG 'amending already signed commit' '
+	git checkout fourth-signed^0 &&
+	git commit --amend -S --no-edit &&
+	git show -s --show-signature HEAD >actual &&
+	grep "Good signature from" actual &&
+	! grep "BAD signature from" actual
+'
+
 test_done

Original file line number	Diff line number	Diff line change
`@@ -1494,7 +1494,8 @@ int cmd_commit(int argc, const char *argv, const char prefix)`
`1494`	`1494`	`}`
`1495`	`1495`
`1496`	`1496`	`if (amend) {`
`1497`		`- extra = read_commit_extra_headers(current_head);`
	`1497`	`+ const char *exclude_gpgsig[2] = { "gpgsig", NULL };`
	`1498`	`+ extra = read_commit_extra_headers(current_head, exclude_gpgsig);`
`1498`	`1499`	`} else {`
`1499`	`1500`	`struct commit_extra_header **tail = &extra;`
`1500`	`1501`	`append_merge_tag_headers(parents, &tail);`