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
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