linux-kernel - [PATCH v2 2/5] string_helpers: add kstrdup_quotable

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Date:	Mon, 28 Mar 2016 14:14:19 -0700
From:	Kees Cook <keescook@...omium.org>
To:	James Morris <jmorris@...ei.org>
Cc:	Kees Cook <keescook@...omium.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kalle Valo <kvalo@...eaurora.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Joe Perches <joe@...ches.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jiri Slaby <jslaby@...e.com>, Paul Moore <pmoore@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Andreas Gruenbacher <agruenba@...hat.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/5] string_helpers: add kstrdup_quotable_cmdline

Provide an escaped (but readable: no inter-argument NULLs) commandline
safe for logging.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/string_helpers.h |  1 +
 lib/string_helpers.c           | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
index 10f535bc9bb5..ee1e8f701eb1 100644
--- a/include/linux/string_helpers.h
+++ b/include/linux/string_helpers.h
@@ -69,5 +69,6 @@ static inline int string_escape_str_any_np(const char *src, char *dst,
 }
 
 char *kstrdup_quotable(char *src);
+char *kstrdup_quotable_cmdline(struct task_struct *task);
 
 #endif
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 9b07c696d709..142bed739fed 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -10,6 +10,7 @@
 #include <linux/export.h>
 #include <linux/ctype.h>
 #include <linux/errno.h>
+#include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/string_helpers.h>
@@ -562,3 +563,37 @@ char *kstrdup_quotable(char *src)
 	return dst;
 }
 EXPORT_SYMBOL_GPL(kstrdup_quotable);
+
+/*
+ * Returns allocated NULL-terminated string containing process
+ * command line, with inter-argument NULLs replaced with spaces,
+ * and other special characters escaped.
+ */
+char *kstrdup_quotable_cmdline(struct task_struct *task)
+{
+	char *buffer, *quoted;
+	int i, res;
+
+	buffer = kmalloc(PAGE_SIZE, GFP_TEMPORARY);
+	if (!buffer)
+		return NULL;
+
+	res = get_cmdline(task, buffer, PAGE_SIZE - 1);
+	buffer[res] = '\0';
+
+	/* Collapse trailing NULLs. */
+	for (; res > 0; res--)
+		if (buffer[res-1] != '\0')
+			break;
+
+	/* Replace inter-argument NULLs. */
+	for (i = 0; i < res; i++)
+		if (buffer[i] == '\0')
+			buffer[i] = ' ';
+
+	/* Make sure result is printable. */
+	quoted = kstrdup_quotable(buffer);
+	kfree(buffer);
+	return quoted;
+}
+EXPORT_SYMBOL_GPL(kstrdup_quotable_cmdline);
-- 
2.6.3