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Date:   Tue, 6 Jun 2023 17:30:33 +0800
From:   Herbert Xu <herbert@gondor.apana.org.au>
To:     David Howells <dhowells@redhat.com>
Cc:     netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
        David Ahern <dsahern@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, linux-crypto@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v2 10/10] crypto: af_alg/hash: Support
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On Tue, Jun 06, 2023 at 10:24:55AM +0100, David Howells wrote:
>
> If the iov_iter is a user-backed type (IOVEC or UBUF) then it's not relaxed.
> max_pages is ALG_MAX_PAGES here (actually, I should just move that here so
> that it's clearer).

Even if it's kernel memory they can't be freed during the hashing
operation, which could be long if the amount is large (or the algo
is slow).

The reason for the limit here is to stop a malicious user from
pinning an unlimited amount of memory by doing a hashing operation,
IOW a DoS attack.

So I think we should keep the limit as is.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt