Re: [PATCH net-next] crypto: af_alg/hash: Fix recvmsg() after sendmsg(MSG_MORE)

Herbert Xu
2023-06-16T10:34:03Z

On Thu, Jun 15, 2023 at 12:27:53AM +0100, David Howells wrote:
>
> If an AF_ALG socket bound to a hashing algorithm is sent a zero-length
> message with MSG_MORE set and then recvmsg() is called without first
> sending another message without MSG_MORE set to end the operation, an oops
> will occur because the crypto context and result doesn't now get set up in
> advance because hash_sendmsg() now defers that as long as possible in the
> hope that it can use crypto_ahash_digest() - and then because the message
> is zero-length, it the data wrangling loop is skipped.
>
> Fix this by always making a pass of the loop, even in the case that no data
> is provided to the sendmsg().
>
> Fix also extract_iter_to_sg() to handle a zero-length iterator by returning
> 0 immediately.
>
> Whilst we're at it, remove the code to create a kvmalloc'd scatterlist if
> we get more than ALG_MAX_PAGES - this shouldn't happen.
>
> Fixes: c662b043cdca ("crypto: af_alg/hash: Support MSG_SPLICE_PAGES")
> Reported-by: syzbot+13a08c0bf4d212766c3c@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/r/000000000000b928f705fdeb873a@google.com/
> Reported-by: syzbot+14234ccf6d0ef629ec1a@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/r/000000000000c047db05fdeb8790@google.com/
> Reported-by: syzbot+4e2e47f32607d0f72d43@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/r/000000000000bcca3205fdeb87fb@google.com/
> Reported-by: syzbot+472626bb5e7c59fb768f@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/r/000000000000b55d8805fdeb8385@google.com/
> Signed-off-by: David Howells <dhowells@redhat.com>
> Tested-by: syzbot+13a08c0bf4d212766c3c@syzkaller.appspotmail.com
> Tested-by: syzbot+14234ccf6d0ef629ec1a@syzkaller.appspotmail.com
> Tested-by: syzbot+4e2e47f32607d0f72d43@syzkaller.appspotmail.com
> Tested-by: syzbot+472626bb5e7c59fb768f@syzkaller.appspotmail.com
> cc: Herbert Xu <herbert@gondor.apana.org.au>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Eric Dumazet <edumazet@google.com>
> cc: Jakub Kicinski <kuba@kernel.org>
> cc: Paolo Abeni <pabeni@redhat.com>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: linux-crypto@vger.kernel.org
> cc: netdev@vger.kernel.org
> ---
> crypto/algif_hash.c | 21 +++++----------------
> lib/scatterlist.c | 2 +-
> 2 files changed, 6 insertions(+), 17 deletions(-)

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>

Thanks,
--
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