Prevent git blame from segfaulting on a missing author name

The human-readable author and committer name can be missing from
commits imported from foreign SCM interfaces.  Make sure we parse
the "author" and "committer" line a bit more leniently and avoid
segfaulting by assuming the name always exists.

Signed-off-by: David Reiss <dreiss@facebook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-blame.c

@@ -1305,6 +1305,7 @@ static void get_ac_line(const char *inbuf, const char *what,
 	error_out:
 		/* Ugh */
 		*tz = "(unknown)";
+		strcpy(person, *tz);
 		strcpy(mail, *tz);
 		*time = 0;
 		return;
@@ -1314,20 +1315,26 @@ static void get_ac_line(const char *inbuf, const char *what,
 	tmp = person;
 	tmp += len;
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (person < tmp && *tmp != ' ')
 		tmp--;
+	if (tmp <= person)
+		goto error_out;
 	*tz = tmp+1;
 	tzlen = (person+len)-(tmp+1);
 
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (person < tmp && *tmp != ' ')
 		tmp--;
+	if (tmp <= person)
+		goto error_out;
 	*time = strtoul(tmp, NULL, 10);
 	timepos = tmp;
 
 	*tmp = 0;
-	while (*tmp != ' ')
+	while (person < tmp && *tmp != ' ')
 		tmp--;
+	if (tmp <= person)
+		return;
 	mailpos = tmp + 1;
 	*tmp = 0;
 	maillen = timepos - tmp;

t/t8003-blame.sh

@@ -144,4 +144,17 @@ test_expect_success 'blame path that used to be a directory' '
 	git blame HEAD^.. -- path
 '
 
+test_expect_success 'blame to a commit with no author name' '
+  TREE=`git rev-parse HEAD:`
+  cat >badcommit <<EOF
+tree $TREE
+author <noname> 1234567890 +0000
+committer David Reiss <dreiss@facebook.com> 1234567890 +0000
+
+some message
+EOF
+  COMMIT=`git hash-object -t commit -w badcommit`
+  git --no-pager blame $COMMIT -- uno >/dev/null
+'
+
 test_done