Re: [PATCH 11/11] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

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On 06/20/2018 07:04 PM, Kees Cook wrote:
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.

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

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

crypto/echainiv.c: In function ‘echainiv_encrypt’:
crypto/echainiv.c:88:1: warning: the frame size of 2120 bytes is larger than 1024 bytes [-Wframe-larger-than=]
crypto/authenc.c: In function ‘crypto_authenc_copy_assoc’:
crypto/authenc.c:197:1: warning: the frame size of 2120 bytes is larger than 1024 bytes [-Wframe-larger-than=]
crypto/authencesn.c: In function ‘crypto_authenc_esn_copy’:
crypto/authencesn.c:194:1: warning: the frame size of 2120 bytes is larger than 1024 bytes [-Wframe-larger-than=]
crypto/algif_aead.c: In function ‘crypto_aead_copy_sgl’:
crypto/algif_aead.c:90:1: warning: the frame size of 2120 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Christophe

---
  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..25294d0089b2 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 (PAGE_SIZE / 8)
+
  #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
/**


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