linux-kernel - Re: [PATCH] crypto: algif

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Date: Fri, 7 Jun 2024 19:41:12 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Alexander Sapozhnikov <alsp705@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH] crypto: algif_aead: deref after NULL

On Thu, Jun 06, 2024 at 09:34:00PM +0300, Alexander Sapozhnikov wrote:
> From: Alexandr Sapozhnikov <alsp705@...il.com>
> 
> After having been compared to a NULL value at algif_aead.c:191, 
> pointer 'tsgl_src' is passed as 2nd parameter in call to function 
> 'crypto_aead_copy_sgl' at algif_aead.c:244, where it is
> dereferenced at algif_aead.c:85.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Signed-off-by: Alexandr Sapozhnikov <alsp705@...il.com>
> ---
>  crypto/algif_aead.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
> index 42493b4..f757907 100644
> --- a/crypto/algif_aead.c
> +++ b/crypto/algif_aead.c
> @@ -191,7 +191,7 @@ static int _aead_recvmsg(struct socket *sock, struct msghdr *msg,
>  		if (tsgl_src)
>  			break;
>  	}
> -	if (processed && !tsgl_src) {
> +	if (processed || !tsgl_src) {

I think this is a false positive.  If processed is zero (which can
only happen for encryption, i.e., a null message), tsgl_src won't
be dereferenced by the Crypto API.  For decryption processed is
never zero as it always contains the authentication tag.

Cheers,
-- 
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