linux-kernel - [PATCH v2] kernel: escape non-ASCII and control characters in printk()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20110623152137.GA2536@albatros>
Date:	Thu, 23 Jun 2011 19:21:37 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	James Morris <jmorris@...ei.org>, Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: [PATCH v2] kernel: escape non-ASCII and control characters in
 printk()

This patch escapes control characters fed to printk() except '\n' and '\t'.

There are numerous printk() instances with user supplied input as "%s"
data, and unprivileged user may craft log messages with substrings
containing control characters via these printk()s.  Control characters
might fool root viewing the logs via tty, e.g. using ^[1A to suppress
the previous log line.

On the testing Samsung Q310 laptop there are no users of chars outside
of the restricted charset. 

v2 - Allow chars with code >127.  Allow tabs.

Reported-by: Solar Designer <solar@...nwall.com>
Signed-off-by: Vasiliy Kulikov <segoon@...nwall.com>
---
 kernel/printk.c |   17 ++++++++++++++++-
 1 files changed, 16 insertions(+), 1 deletions(-)

---
diff --git a/kernel/printk.c b/kernel/printk.c
index 3518539..727ff7d 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -41,6 +41,7 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/rculist.h>
+#include <linux/ctype.h>
 
 #include <asm/uaccess.h>
 
@@ -671,6 +672,20 @@ static void emit_log_char(char c)
 		logged_chars++;
 }
 
+static void emit_log_char_escaped(char c)
+{
+	char buffer[8];
+	int i, len;
+
+	if (!iscntrl(c) || (c == '\n') || (c == '\t'))
+		emit_log_char(c);
+	else {
+		len = sprintf(buffer, "#x%02x", c);
+		for (i = 0; i < len; i++)
+			emit_log_char(buffer[i]);
+	}
+}
+
 /*
  * Zap console related locks when oopsing. Only zap at most once
  * every 10 seconds, to leave time for slow consoles to print a
@@ -938,7 +953,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 				break;
 		}
 
-		emit_log_char(*p);
+		emit_log_char_escaped(*p);
 		if (*p == '\n')
 			new_text_line = 1;
 	}
---
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/