linux-kernel - [PATCH 3/4] lib/vsprintf.c: Don't try to fix pointer wrap-around

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Date:	Thu,  8 Jan 2015 13:14:46 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Randy Dunlap <rdunlap@...radead.org>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] lib/vsprintf.c: Don't try to fix pointer wrap-around

Actual kernel buffers can't wrap into the user address space. If
someone manages to pass a buf/size combination that wraps, it is most
likely due to a bug in the caller. Instead of trying to fix it by
using a smaller part of the buffer, bail out.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 lib/vsprintf.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index cf12ba86205c..1ec6a78f169b 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1733,11 +1733,9 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
 	str = buf;
 	end = buf + size;
 
-	/* Make sure end is always >= buf */
-	if (end < buf) {
-		end = ((void *)-1);
-		size = end - buf;
-	}
+	/* Also bail out if buf+size wraps */
+	if (WARN_ON_ONCE(end < buf))
+		return 0;
 
 	while (*fmt) {
 		const char *old_fmt = fmt;
-- 
2.1.3

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