linux-kernel - Re: [RFC PATCH] crypto: add buffer overflow checks to testmgr

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Date:	Fri, 29 May 2009 15:27:36 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [RFC PATCH] crypto: add buffer overflow checks to testmgr

On Fri, May 29, 2009 at 11:32:54AM -0400, Jarod Wilson wrote:
> At present, its entirely possible to add a test vector to testmgr with
> an input longer than a page in length w/o specifying a .np option, and
> overflow the page of memory allocated to {a,}xbuf[0], silently
> corrupting memory. I know, because I've accidentally done it. :)
> 
> While this doesn't currently happen in practice w/the existing code,
> due to all !np vectors being less than a 4k page in length (and the
> page allocation loop often returns contiguous pages anyway), explicit
> checks or a way to remove the 4k limit would be a good idea.
> 
> A few ways to fix and/or work around this:
> 
> 1) allocate some larger guaranteed contiguous buffers using
> __get_free_pages() or kmalloc and use them in the !np case
> 
> 2) catch the > PAGE_SIZE && !np case and then do things similar to how
> they are done in the np case
> 
> 3) catch the > PAGE_SIZE && !np case and simply exit with an error
> 
> Since there currently aren't any test vectors that are actually larger
> than a page and not tagged np, option 1 seems like a waste of memory
> and option 2 sounds like unnecessary complexity, so I'd offer up
> option 3 as the most viable alternative right now.
> 
> Signed-off-by: Jarod Wilson <jarod@...hat.com>
> 

Given the rate at which test vectors are added to the testmgr, and the
likelyhood one will be over a page in size, I think this is probably the best
way forward.  Its saves memory/complexity until for now, and catches anyone
trying to exceed the current 1 page size, at which point we can spend the time
to modify the testmanager to make use of scatter/gather chains to handle the
longer vectors.

Neil

Acked-by: Neil Horman <nhorman@...driver.com>

> ---
>  crypto/testmgr.c |   34 ++++++++++++++++++++++++++++++++++
>  1 files changed, 34 insertions(+), 0 deletions(-)
> 
> diff --git a/crypto/testmgr.c b/crypto/testmgr.c
> index 376ea88..9483a2b 100644
> --- a/crypto/testmgr.c
> +++ b/crypto/testmgr.c
> @@ -185,6 +185,13 @@ static int test_hash(struct crypto_ahash *tfm, struct hash_testvec *template,
>  
>  		hash_buff = xbuf[0];
>  
> +		if (template[i].psize > PAGE_SIZE) {
> +			printk(KERN_ERR "alg: hash: psize %u larger than "
> +			       "contiguous buffer space\n", template[i].psize);
> +			ret = -EOVERFLOW;
> +			goto out;
> +		}
> +
>  		memcpy(hash_buff, template[i].plaintext, template[i].psize);
>  		sg_init_one(&sg[0], hash_buff, template[i].psize);
>  
> @@ -357,6 +364,16 @@ static int test_aead(struct crypto_aead *tfm, int enc,
>  			input = xbuf[0];
>  			assoc = axbuf[0];
>  
> +			if (template[i].ilen > PAGE_SIZE ||
> +			    template[i].alen > PAGE_SIZE) {
> +				printk(KERN_ERR "alg: aead: input larger than "
> +				       "contiguous buffer space (ilen: %u, "
> +				       "alen: %u)\n",
> +				       template[i].ilen, template[i].alen);
> +				ret = -EOVERFLOW;
> +				goto out;
> +			}
> +
>  			memcpy(input, template[i].input, template[i].ilen);
>  			memcpy(assoc, template[i].assoc, template[i].alen);
>  			if (template[i].iv)
> @@ -651,6 +668,14 @@ static int test_cipher(struct crypto_cipher *tfm, int enc,
>  		j++;
>  
>  		data = xbuf[0];
> +
> +		if (template[i].ilen > PAGE_SIZE) {
> +			printk(KERN_ERR "alg: cipher: ilen %u larger than "
> +			       "contiguous buffer space\n", template[i].ilen);
> +			ret = -EOVERFLOW;
> +			goto out;
> +		}
> +
>  		memcpy(data, template[i].input, template[i].ilen);
>  
>  		crypto_cipher_clear_flags(tfm, ~0);
> @@ -742,6 +767,15 @@ static int test_skcipher(struct crypto_ablkcipher *tfm, int enc,
>  			j++;
>  
>  			data = xbuf[0];
> +
> +			if (template[i].ilen > PAGE_SIZE) {
> +				printk(KERN_ERR "alg: skcipher: ilen %u larger "
> +				       "than contiguous buffer space\n",
> +				       template[i].ilen);
> +				ret = -EOVERFLOW;
> +				goto out;
> +			}
> +
>  			memcpy(data, template[i].input, template[i].ilen);
>  
>  			crypto_ablkcipher_clear_flags(tfm, ~0);
> 
> -- 
> Jarod Wilson
> jarod@...hat.com
> 
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