[PATCH 2/2] commit: reject overlong UTF-8 sequences

["brian m. carlson" <sandals@xxxxxxxxxxxxxxxxxxxx>]

The commit code accepts pseudo-UTF-8 sequences that encode a character with more
bytes than necessary.  Reject such sequences, since they are not valid UTF-8.

Signed-off-by: brian m. carlson <sandals@xxxxxxxxxxxxxxxxxxxx>
---
 commit.c                   | 14 ++++++++++++--
 t/t3900-i18n-commit.sh     |  8 ++++++++
 t/t3900/UTF-8-overlong.txt |  3 +++
 3 files changed, 23 insertions(+), 2 deletions(-)
 create mode 100644 t/t3900/UTF-8-overlong.txt

diff --git a/commit.c b/commit.c
index 2280413..e57fec6 100644
--- a/commit.c
+++ b/commit.c
@@ -1240,11 +1240,15 @@ int commit_tree(const struct strbuf *msg, unsigned char *tree,
 static int find_invalid_utf8(const char *buf, int len)
 {
 	int offset = 0;
+	static const unsigned int max_codepoint[] = {
+		0x7f, 0x7ff, 0xffff, 0x1fffff
+	};
 
 	while (len) {
 		unsigned char c = *buf++;
 		int bytes, bad_offset;
 		unsigned int codepoint;
+		unsigned int min_val, max_val;
 
 		len--;
 		offset++;
@@ -1273,8 +1277,12 @@ static int find_invalid_utf8(const char *buf, int len)
 		if (len < bytes)
 			return bad_offset;
 
-		/* Place the encoded bits at the bottom of the value. */
+		/* Place the encoded bits at the bottom of the value and compute the
+		 * valid range.
+		 */
 		codepoint = (c & 0x7f) >> bytes;
+		min_val = max_codepoint[bytes-1] + 1;
+		max_val = max_codepoint[bytes];
 
 		offset += bytes;
 		len -= bytes;
@@ -1287,13 +1295,15 @@ static int find_invalid_utf8(const char *buf, int len)
 				return bad_offset;
 		} while (--bytes);
 
-		/* Check the value here */
+		/* Check the value and length here */
 		if (codepoint >= 0xd800 && codepoint <= 0xdfff)
 			return bad_offset;
 		if (codepoint > 0x10ffff)
 			return bad_offset;
 		if ((codepoint & 0x1ffffe) == 0xfffe)
 			return bad_offset;
+		if (codepoint < min_val || codepoint > max_val)
+			return bad_offset;
 	}
 	return -1;
 }
diff --git a/t/t3900-i18n-commit.sh b/t/t3900-i18n-commit.sh
index 16ed707..de0fcef 100755
--- a/t/t3900-i18n-commit.sh
+++ b/t/t3900-i18n-commit.sh
@@ -47,6 +47,14 @@ test_expect_success 'UTF-8 invalid characters refused' '
 	grep "did not conform" "$HOME"/stderr
 '
 
+test_expect_success 'UTF-8 overlong sequences rejected' '
+	rm -f "$HOME/stderr" &&
+	echo "UTF-8 overlong" >F &&
+	git commit -a -F "$TEST_DIRECTORY"/t3900/UTF-8-overlong.txt \
+		2>"$HOME"/stderr &&
+	grep "did not conform" "$HOME"/stderr
+'
+
 rm -f "$HOME/stderr"
 
 for H in ISO8859-1 eucJP ISO-2022-JP
diff --git a/t/t3900/UTF-8-overlong.txt b/t/t3900/UTF-8-overlong.txt
new file mode 100644
index 0000000..fa157e9
--- /dev/null
+++ b/t/t3900/UTF-8-overlong.txt
@@ -0,0 +1,3 @@
+???ommit message
+
+This is not a space:??
-- 
1.8.3.1
--
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