linux-kernel - Re: [PATCH] crypto: af_alg - Work around empty control messages without MSG

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Message-ID: <CAMj1kXHCazXbeTDfcjD=rUyLVcOqrHcHqfgOnsDWt51dALfSpg@mail.gmail.com>
Date:   Wed, 26 Aug 2020 15:56:20 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Andrew Zaborowski <andrew.zaborowski@...el.com>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        Caleb Jorden <caljorden@...mail.com>,
        Sasha Levin <sashal@...nel.org>, iwd@...ts.01.org,
        "# 3.4.x" <stable@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH] crypto: af_alg - Work around empty control messages
 without MSG_MORE

On Wed, 26 Aug 2020 at 15:30, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> The iwd daemon uses libell which sets up the skcipher operation with
> two separate control messages.  This is fine by itself but the first
> control message is sent without MSG_MORE.  This means that the first
> control message is interpreted as an empty request.
>
> While libell should be fixed to use MSG_MORE where appropriate, this
> patch works around the bug in the kernel so that existing binaries
> continue to work.
>
> We will print a warning however.
>
> Reported-by: Caleb Jorden <caljorden@...mail.com>
> Fixes: f3c802a1f300 ("crypto: algif_aead - Only wake up when...")
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
>

Applied this onto v5.4.60, and it makes the iwd selftests pass again

Acked-by: Ard Biesheuvel <ardb@...nel.org>
Tested-by: Ard Biesheuvel <ardb@...nel.org>

> diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> index a6f581ab200c..3da21cadc326 100644
> --- a/crypto/af_alg.c
> +++ b/crypto/af_alg.c
> @@ -16,6 +16,7 @@
>  #include <linux/module.h>
>  #include <linux/net.h>
>  #include <linux/rwsem.h>
> +#include <linux/sched.h>
>  #include <linux/sched/signal.h>
>  #include <linux/security.h>
>
> @@ -846,8 +847,14 @@ int af_alg_sendmsg(struct socket *sock, struct msghdr *msg, size_t size,
>
>         lock_sock(sk);
>         if (ctx->init && (init || !ctx->more)) {
> -               err = -EINVAL;
> -               goto unlock;
> +               if (ctx->used) {
> +                       err = -EINVAL;
> +                       goto unlock;
> +               }
> +
> +               pr_info_once(
> +                       "%s sent an empty control message without MSG_MORE.\n",
> +                       current->comm);
>         }
>         ctx->init = true;
>
> --
> Email: Herbert Xu <herbert@...dor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt