linux-kernel - Re: [PATCH 4.5 079/238] crypto: ccp - Dont assume export/import areas are aligned

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Message-ID: <1460426212.25201.98.camel@decadent.org.uk>
Date:	Tue, 12 Apr 2016 02:56:52 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Cc:	stable@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH 4.5 079/238] crypto: ccp - Dont assume export/import
 areas are aligned

On Sun, 2016-04-10 at 11:34 -0700, Greg Kroah-Hartman wrote:
> 4.5-stable review patch.  If anyone has any objections, please let me know.

I object, because this introduces an information leak.

[...]
> --- a/drivers/crypto/ccp/ccp-crypto-sha.c
> +++ b/drivers/crypto/ccp/ccp-crypto-sha.c
> @@ -210,14 +210,17 @@ static int ccp_sha_digest(struct ahash_r
>  static int ccp_sha_export(struct ahash_request *req, void *out)
>  {
>  	struct ccp_sha_req_ctx *rctx = ahash_request_ctx(req);
> -	struct ccp_sha_exp_ctx *state = out;
> +	struct ccp_sha_exp_ctx state;

The structure was defined in the previous patch as:

> +struct ccp_sha_exp_ctx {
> +	enum ccp_sha_type type;

There will be padding between type and msg_bits on most architectures.

> +	u64 msg_bits;
> +	unsigned int first;
> +
> +	u8 ctx[MAX_SHA_CONTEXT_SIZE];
> +
> +	unsigned int buf_count;
> +	u8 buf[MAX_SHA_BLOCK_SIZE];

And more padding at the end of the structure.

> +};

Back to the code:

> -	state->type = rctx->type;
> -	state->msg_bits = rctx->msg_bits;
> -	state->first = rctx->first;
> -	memcpy(state->ctx, rctx->ctx, sizeof(state->ctx));
> -	state->buf_count = rctx->buf_count;
> -	memcpy(state->buf, rctx->buf, sizeof(state->buf));
> +	state.type = rctx->type;
> +	state.msg_bits = rctx->msg_bits;
> +	state.first = rctx->first;
> +	memcpy(state.ctx, rctx->ctx, sizeof(state.ctx));
> +	state.buf_count = rctx->buf_count;
> +	memcpy(state.buf, rctx->buf, sizeof(state.buf));
> +
> +	/* 'out' may not be aligned so memcpy from local variable */
> +	memcpy(out, &state, sizeof(state));
[...]

The padding was not initialised, but here we copy it to userland.

Ben.

-- 
Ben Hutchings
This sentence contradicts itself - no actually it doesn't.
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