sideband: introduce an "escape hatch" to allow control characters

The preceding commit fixed the vulnerability whereas sideband messages
(that are under the control of the remote server) could contain ANSI
escape sequences that would be sent to the terminal verbatim.

However, this fix may not be desirable under all circumstances, e.g.
when remote servers deliberately add coloring to their messages to
increase their urgency.

To help with those use cases, give users a way to opt-out of the
protections: `sideband.allowControlCharacters`.

Suggested-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/config.adoc b/Documentation/config.adoc
index 62eebe7..dcea3c0 100644 (file)
--- a/Documentation/config.adoc
+++ b/Documentation/config.adoc
@@ -523,6 +523,8 @@ include::config/sequencer.adoc[]
 
 include::config/showbranch.adoc[]
 
+include::config/sideband.adoc[]
+
 include::config/sparse.adoc[]
 
 include::config/splitindex.adoc[]

diff --git a/Documentation/config/sideband.adoc b/Documentation/config/sideband.adoc
new file mode 100644 (file)
index 0000000..3fb5045
--- /dev/null
+++ b/Documentation/config/sideband.adoc
@@ -0,0 +1,5 @@
+sideband.allowControlCharacters::
+       By default, control characters that are delivered via the sideband
+       are masked, to prevent potentially unwanted ANSI escape sequences
+       from being sent to the terminal. Use this config setting to override
+       this behavior.

diff --git a/sideband.c b/sideband.c
index c1bbadc..682f1cb 100644 (file)
--- a/sideband.c
+++ b/sideband.c
@@ -26,6 +26,8 @@ static struct keyword_entry keywords[] = {
        { "error",      GIT_COLOR_BOLD_RED },
 };
 
+static int allow_control_characters;
+
 /* Returns a color setting (GIT_COLOR_NEVER, etc). */
 static enum git_colorbool use_sideband_colors(void)
 {
@@ -39,6 +41,9 @@ static enum git_colorbool use_sideband_colors(void)
        if (use_sideband_colors_cached != GIT_COLOR_UNKNOWN)
                return use_sideband_colors_cached;
 
+       repo_config_get_bool(the_repository, "sideband.allowcontrolcharacters",
+                           &allow_control_characters);
+
        if (!repo_config_get_string_tmp(the_repository, key, &value))
                use_sideband_colors_cached = git_config_colorbool(key, value);
        else if (!repo_config_get_string_tmp(the_repository, "color.ui", &value))
@@ -68,6 +73,11 @@ void list_config_color_sideband_slots(struct string_list *list, const char *pref
 
 static void strbuf_add_sanitized(struct strbuf *dest, const char *src, int n)
 {
+       if (allow_control_characters) {
+               strbuf_add(dest, src, n);
+               return;
+       }
+
        strbuf_grow(dest, n);
        for (; n && *src; src++, n--) {
                if (!iscntrl(*src) || *src == '\t' || *src == '\n') {

diff --git a/t/t5409-colorize-remote-messages.sh b/t/t5409-colorize-remote-messages.sh
index aa5b570..9caee9a 100755 (executable)
--- a/t/t5409-colorize-remote-messages.sh
+++ b/t/t5409-colorize-remote-messages.sh
@@ -105,9 +105,15 @@ test_expect_success 'disallow (color) control sequences in sideband' '
        EOF
        test_config_global uploadPack.packObjectsHook ./color-me-surprised &&
        test_commit need-at-least-one-commit &&
+
        git clone --no-local . throw-away 2>stderr &&
        test_decode_color <stderr >decoded &&
-       test_grep ! RED decoded
+       test_grep ! RED decoded &&
+
+       rm -rf throw-away &&
+       git -c sideband.allowControlCharacters clone --no-local . throw-away 2>stderr &&
+       test_decode_color <stderr >decoded &&
+       test_grep RED decoded
 '
 
 test_done