linux-kernel - [PATCH] vsprintf: Remove %n handling

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <52E826D4.8020008@gmail.com>
Date:	Wed, 29 Jan 2014 08:53:24 +1100
From:	Ryan Mallon <rmallon@...il.com>
To:	kees Cook <keescook@...omium.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Joe Perches <joe@...ches.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Olof Johansson <olof@...om.net>,
	Stepan Moskovchenko <stepanm@...eaurora.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] vsprintf: Remove %n handling

All in kernel users of %n in format strings have now been removed and
the %n directive is ignored. Remove the handling of %n so that it is
treated the same as any other invalid format string directive. Keep a
warning in place to deter new instances of %n in format strings.

Signed-off-by: Ryan Mallon <rmallon@...il.com>
Acked-by: Kees Cook <keescook@...omium.org>
---

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 10909c5..7c4c207 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -364,7 +364,6 @@ enum format_type {
 	FORMAT_TYPE_SHORT,
 	FORMAT_TYPE_UINT,
 	FORMAT_TYPE_INT,
-	FORMAT_TYPE_NRCHARS,
 	FORMAT_TYPE_SIZE_T,
 	FORMAT_TYPE_PTRDIFF
 };
@@ -1512,10 +1511,6 @@ qualifier:
 		return fmt - start;
 		/* skip alnum */
 
-	case 'n':
-		spec->type = FORMAT_TYPE_NRCHARS;
-		return ++fmt - start;
-
 	case '%':
 		spec->type = FORMAT_TYPE_PERCENT_CHAR;
 		return ++fmt - start;
@@ -1538,6 +1533,15 @@ qualifier:
 	case 'u':
 		break;
 
+	case 'n':
+		/*
+		 * Since %n poses a greater security risk than utility, treat
+		 * it as an invalid format specifier. Warn about its use so
+		 * that new instances don't get added.
+		 */
+		WARN_ONCE(1, "Please remove ignored %%n in '%s'\n", fmt);
+		/* Fall-through */
+
 	default:
 		spec->type = FORMAT_TYPE_INVALID;
 		return fmt - start;
@@ -1711,20 +1715,6 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
 			++str;
 			break;
 
-		case FORMAT_TYPE_NRCHARS: {
-			/*
-			 * Since %n poses a greater security risk than
-			 * utility, ignore %n and skip its argument.
-			 */
-			void *skip_arg;
-
-			WARN_ONCE(1, "Please remove ignored %%n in '%s'\n",
-					old_fmt);
-
-			skip_arg = va_arg(args, void *);
-			break;
-		}
-
 		default:
 			switch (spec.type) {
 			case FORMAT_TYPE_LONG_LONG:
@@ -1999,19 +1989,6 @@ do {									\
 				fmt++;
 			break;
 
-		case FORMAT_TYPE_NRCHARS: {
-			/* skip %n 's argument */
-			u8 qualifier = spec.qualifier;
-			void *skip_arg;
-			if (qualifier == 'l')
-				skip_arg = va_arg(args, long *);
-			else if (_tolower(qualifier) == 'z')
-				skip_arg = va_arg(args, size_t *);
-			else
-				skip_arg = va_arg(args, int *);
-			break;
-		}
-
 		default:
 			switch (spec.type) {
 
@@ -2170,10 +2147,6 @@ int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf)
 			++str;
 			break;
 
-		case FORMAT_TYPE_NRCHARS:
-			/* skip */
-			break;
-
 		default: {
 			unsigned long long num;
 

--
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/