[PATCH 2/2] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK
From: Ard Biesheuvel <hidden>
Date: 2018-09-05 09:18:10
Also in:
linux-crypto, lkml
On 4 September 2018 at 20:16, Kees Cook [off-list ref] 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. 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: 472Are you sure this is a representative sampling? I haven't double checked myself, but we have plenty of drivers for peripherals in drivers/crypto that implement block ciphers, and they would not turn up in tcrypt unless you are running on a platform that provides the hardware in question.
quoted hunk ↗ jump to hunk
[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA at mail.gmail.com Signed-off-by: Kees Cook <redacted> --- 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