daemon: fix off-by-one in logging extended attributes

If receive a request like:

  git-upload-pack /foo.git\0host=localhost

we mark the offset of the NUL byte as "len", and then log
the bytes after the NUL with a "%.*s" placeholder, using
"pktlen - len" as the length, and "line + len + 1" as the
start of the string.

This is off-by-one, since the start of the string skips past
the separating NUL byte, but the adjusted length includes
it. Fortunately this doesn't actually read past the end of
the buffer, since "%.*s" will stop when it hits a NUL. And
regardless of what is in the buffer, packet_read() will
always add an extra NUL terminator for safety.

As an aside, the git.git client sends an extra NUL after a
"host" field, too, so we'd generally hit that one first, not
the one added by packet_read(). You can see this in the test
output which reports 15 bytes, even though the string has
only 14 bytes of visible data. But the point is that even a
client sending unusual data could not get us to read past
the end of the buffer, so this is purely a cosmetic fix.

Reported-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

daemon.c

@@ -759,8 +759,8 @@ static int execute(void)
 	len = strlen(line);
 	if (pktlen != len)
 		loginfo("Extended attributes (%d bytes) exist <%.*s>",
-			(int) pktlen - len,
-			(int) pktlen - len, line + len + 1);
+			(int) pktlen - len - 1,
+			(int) pktlen - len - 1, line + len + 1);
 	if (len && line[len-1] == '\n') {
 		line[--len] = 0;
 		pktlen--;

t/t5570-git-daemon.sh

@@ -183,5 +183,16 @@ test_expect_success 'hostname cannot break out of directory' '
 		git ls-remote "$GIT_DAEMON_URL/escape.git"
 '
 
+test_expect_success 'daemon log records hostnames' '
+	cat >expect <<-\EOF &&
+	Extended attributes (15 bytes) exist <host=localhost>
+	EOF
+	>daemon.log &&
+	GIT_OVERRIDE_VIRTUAL_HOST=localhost \
+		git ls-remote "$GIT_DAEMON_URL/interp.git" &&
+	grep -i extended.attribute daemon.log | cut -d" " -f2- >actual &&
+	test_cmp expect actual
+'
+
 stop_git_daemon
 test_done