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Subject[PATCH v8 9/9] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK
Date
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@chromium.org>
---
include/crypto/internal/skcipher.h | 1 +
include/crypto/skcipher.h | 4 +++-
2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/crypto/internal/skcipher.h b/include/crypto/internal/skcipher.h
index e42f7063f245..5035482cbe68 100644
--- a/include/crypto/internal/skcipher.h
+++ b/include/crypto/internal/skcipher.h
@@ -130,6 +130,7 @@ static inline struct crypto_skcipher *crypto_spawn_skcipher(
static inline void crypto_skcipher_set_reqsize(
struct crypto_skcipher *skcipher, unsigned int reqsize)
{
+ BUG_ON(reqsize > SKCIPHER_MAX_REQSIZE);
skcipher->reqsize = reqsize;
}

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
\
 
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