[PATCH v2] xenconsole: add option to avoid escape sequences in log

* [PATCH v2] xenconsole: add option to avoid escape sequences in log
@ 2018-07-31  3:15 Marek Marczykowski-Górecki
  2018-07-31  9:10 ` Wei Liu
  0 siblings, 1 reply; 3+ messages in thread
From: Marek Marczykowski-Górecki @ 2018-07-31  3:15 UTC (permalink / raw)
  To: xen-devel
  Cc: Wei Liu, Ian Jackson, Marek Marczykowski-Górecki, xen-devel

Add --replace-escape option to xenconsoled, which replaces ESC with
'.' in console output written to log file. This makes it slightly safer
to do tail -f on a console output of untrusted guest.
The pty output is unaffected by this option.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
Changes in v2:
 - optimize do_replace_escape() per Wei's suggestion
 - expand help string
 - avoid variable sized array on stack per Christopher's suggestion
   (although this made the code a little more ugly :/ - I try hard to
    not impact performance when this option is disabled)
---
 tools/console/daemon/io.c   | 27 ++++++++++++++++++++++++++-
 tools/console/daemon/main.c |  8 +++++++-
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
index e22009aa39..1457b954fa 100644
--- a/tools/console/daemon/io.c
+++ b/tools/console/daemon/io.c
@@ -68,6 +68,7 @@ extern int log_time_hv;
 extern int log_time_guest;
 extern char *log_dir;
 extern int discard_overflowed_data;
+extern int replace_escape;
 
 static int log_time_hv_needts = 1;
 static int log_time_guest_needts = 1;
@@ -227,10 +228,34 @@ static inline int console_iter_int_arg3(struct domain *d,
 	return ret;
 }
 
+static void do_replace_escape(const char *src, char *dest, int len)
+{
+	int i;
+
+	for (i = 0; i < len; i++) {
+		if (src[i] == '\033')
+			dest[i] = '.';
+		else
+			dest[i] = src[i];
+	}
+}
+
 static int write_all(int fd, const char* buf, size_t len)
 {
+	char buf_replaced[1024];
+	size_t this_round;
+
 	while (len) {
-		ssize_t ret = write(fd, buf, len);
+		ssize_t ret;
+		if (replace_escape) {
+			if (len > sizeof(buf_replaced))
+				this_round = sizeof(buf_replaced);
+			else
+				this_round = len;
+			do_replace_escape(buf, buf_replaced, this_round);
+			ret = write(fd, buf_replaced, this_round);
+		} else
+			ret = write(fd, buf, len);
 		if (ret == -1 && errno == EINTR)
 			continue;
 		if (ret <= 0)
diff --git a/tools/console/daemon/main.c b/tools/console/daemon/main.c
index 806d2fd611..5d9d55b430 100644
--- a/tools/console/daemon/main.c
+++ b/tools/console/daemon/main.c
@@ -40,6 +40,7 @@ int log_time_hv = 0;
 int log_time_guest = 0;
 char *log_dir = NULL;
 int discard_overflowed_data = 1;
+int replace_escape = 0;
 
 static void handle_hup(int sig)
 {
@@ -48,7 +49,8 @@ static void handle_hup(int sig)
 
 static void usage(char *name)
 {
-	printf("Usage: %s [-h] [-V] [-v] [-i] [--log=none|guest|hv|all] [--log-dir=DIR] [--pid-file=PATH] [-t, --timestamp=none|guest|hv|all] [-o, --overflow-data=discard|keep]\n", name);
+	printf("Usage: %s [-h] [-V] [-v] [-i] [--log=none|guest|hv|all] [--log-dir=DIR] [--pid-file=PATH] [-t, --timestamp=none|guest|hv|all] [-o, --overflow-data=discard|keep] [--replace-escape]\n", name);
+	printf("  --replace-escape  - replace ESC character with dot when writing console log\n");
 }
 
 static void version(char *name)
@@ -104,6 +106,7 @@ int main(int argc, char **argv)
 		{ "pid-file", 1, 0, 'p' },
 		{ "timestamp", 1, 0, 't' },
 		{ "overflow-data", 1, 0, 'o'},
+		{ "replace-escape", 0, 0, 'e'},
 		{ 0 },
 	};
 	bool is_interactive = false;
@@ -168,6 +171,9 @@ int main(int argc, char **argv)
 				discard_overflowed_data = 1;
 			}
 			break;
+		case 'e':
+			replace_escape = 1;
+			break;
 		case '?':
 			fprintf(stderr,
 				"Try `%s --help' for more information\n",
-- 
2.17.1


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