linux-kernel - [PATCH 2/2] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON

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Date:   Tue,  4 Sep 2018 11:16:29 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Kees Cook <keescook@...omium.org>,
        Eric Biggers <ebiggers@...gle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Arnaud Ebalard <arno@...isbad.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Christian Lamparter <chunkeey@...il.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 2/2] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

In the quest to remove all stack VLA usage from the kernel[1], this
caps the skcipher request size similar to other limits and adds a sanity
check at registration. Looking at instrumented tcrypt output, the largest
is for lrw:

	crypt: testing lrw(aes)
	crypto_skcipher_set_reqsize: 8
	crypto_skcipher_set_reqsize: 88
	crypto_skcipher_set_reqsize: 472

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/crypto/internal/skcipher.h | 3 +++
 include/crypto/skcipher.h          | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/crypto/internal/skcipher.h b/include/crypto/internal/skcipher.h
index d2926ecae2ac..6da811c0747e 100644
--- a/include/crypto/internal/skcipher.h
+++ b/include/crypto/internal/skcipher.h
@@ -130,6 +130,9 @@ static inline struct crypto_skcipher *crypto_spawn_skcipher(
 static inline int crypto_skcipher_set_reqsize(
 	struct crypto_skcipher *skcipher, unsigned int reqsize)
 {
+	if (WARN_ON(reqsize > SKCIPHER_MAX_REQSIZE))
+		return -EINVAL;
+
 	skcipher->reqsize = reqsize;
 
 	return 0;
diff --git a/include/crypto/skcipher.h b/include/crypto/skcipher.h
index 2f327f090c3e..c48e194438cf 100644
--- a/include/crypto/skcipher.h
+++ b/include/crypto/skcipher.h
@@ -139,9 +139,11 @@ struct skcipher_alg {
 	struct crypto_alg base;
 };
 
+#define SKCIPHER_MAX_REQSIZE	472
+
 #define SKCIPHER_REQUEST_ON_STACK(name, tfm) \
 	char __##name##_desc[sizeof(struct skcipher_request) + \
-		crypto_skcipher_reqsize(tfm)] CRYPTO_MINALIGN_ATTR; \
+		SKCIPHER_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \
 	struct skcipher_request *name = (void *)__##name##_desc
 
 /**
-- 
2.17.1