Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH net-next] crypto: af_alg/hash: Fix recvmsg() after sendmsg(MSG_MORE) | Date | Mon, 19 Jun 2023 17:47:26 +0100 |
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Herbert Xu <herbert@gondor.apana.org.au> wrote:
> Anyway, why did you remove the condition on hash_free_result? > We free the result if it's not needed, not to clear the previous > hash. So by doing it uncondtionally you will simply end up > freeing and reallocating the result for no good reason.
The free here:
if (!continuing) { if ((msg->msg_flags & MSG_MORE)) hash_free_result(sk, ctx);
only happens in the following case:
send(hashfd, "", 0, 0); send(hashfd, "", 0, MSG_MORE); <--- by this
and the patch changes how this case works if no data is given. In Linus's tree, it will create a result, init the crypto and finalise it in hash_sendmsg(); with this patch that case is then handled by hash_recvmsg(). If you consider the following sequence:
send(hashfd, "", 0, 0); send(hashfd, "", 0, 0); send(hashfd, "", 0, 0); send(hashfd, "", 0, 0);
Upstream, the first one will create a result and then each of them will init and finalise a hash, whereas with my patch, the first one will release any outstanding result and then none of them will do any crypto ops.
However, as, with my patch hash_sendmsg() no longer calculated a result, it has to clear the result pointer because the logic inside hash_recvmsg() relies on the result pointer to indicate that there is a result.
Instead, hash_recvmsg() concocts the result - something it has to be able to do anyway in case someone calls recvmsg() without first supplying data.
David
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