linux-kernel - [PATCH] strscpy: reject buffer sizes larger than INT

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Message-ID: <201907260928.23DE35406@keescook>
Date:   Fri, 26 Jul 2019 09:31:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Joe Perches <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Yann Droneaud <ydroneaud@...eya.com>,
        David Laight <David.Laight@...lab.com>,
        Jonathan Corbet <corbet@....net>, Stephen Kitt <steve@....org>,
        Nitin Gote <nitin.r.gote@...el.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: [PATCH] strscpy: reject buffer sizes larger than INT_MAX

As already done for snprintf(), add a check in strscpy() for giant
(i.e. likely negative and/or miscalculated) copy sizes, WARN, and
error out.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 lib/string.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/string.c b/lib/string.c
index 461fb620f85f..913cb945a82a 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -182,7 +182,7 @@ ssize_t strscpy(char *dest, const char *src, size_t count)
 	size_t max = count;
 	long res = 0;
 
-	if (count == 0)
+	if (count == 0 || WARN_ON_ONCE(count > INT_MAX))
 		return -E2BIG;
 
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
-- 
2.17.1


-- 
Kees Cook