[v5,11/11] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

Commit Message

Kees Cook July 17, 2018, 4:21 a.m. UTC

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=[e-mail]

Signed-off-by: Kees Cook <[e-mail]>
---
 include/crypto/internal/skcipher.h | 1 +
 include/crypto/skcipher.h          | 4 +++-
 2 files changed, 4 insertions(+), 1 deletion(-)

Patch

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
 
 /**