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

[Greg Kroah-Hartman]

On Tue, Apr 12, 2016 at 02:56:52AM +0100, Ben Hutchings wrote:
> 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.

Nice catch.  Given that the user/kernel structure here doesn't seem very
sane (implicit padding, etc.), shouldn't that be where this is fixed up
to be a properly packed structure?  Or have padding where needed, along
with a memset() call?

I'll leave this here, but will be expecting a follow-on patch to fix up
the issues from the crypto developers.

thanks,

greg k-h