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From:   Sven Schnelle <svens@linux.ibm.com>
To:     David Howells <dhowells@redhat.com>
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        <omosnacek@gmail.com>, Herbert Xu <herbert@gondor.apana.org.au>,
        Paolo Abeni <pabeni@redhat.com>,
        Harald Freudenberger <freude@linux.vnet.ibm.com>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        linux-crypto@vger.kernel.org, linux-s390@vger.kernel.org,
        netdev@vger.kernel.org, regressions@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] crypto: Fix missing initialisation affecting gcm-aes-s390
References: <CAAUqJDuRkHE8fPgZJGaKjUjd3QfGwzfumuJBmStPqBhubxyk_A@mail.gmail.com>
        <97730.1690408399@warthog.procyon.org.uk>
Date:   Thu, 27 Jul 2023 07:55:18 +0200
In-Reply-To: <97730.1690408399@warthog.procyon.org.uk> (David Howells's
        message of "Wed, 26 Jul 2023 22:53:19 +0100")
Message-ID: <yt9dbkfxsxtl.fsf@linux.ibm.com>
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David Howells <dhowells@redhat.com> writes:

>=20=20=20=20=20
> Fix af_alg_alloc_areq() to initialise areq->first_rsgl.sgl.sgt.sgl to poi=
nt
> to the scatterlist array in areq->first_rsgl.sgl.sgl.
>
> Without this, the gcm-aes-s390 driver will oops when it tries to do
> gcm_walk_start() on req->dst because req->dst is set to the value of
> areq->first_rsgl.sgl.sgl by _aead_recvmsg() calling
> aead_request_set_crypt().
>
> The problem comes if an empty ciphertext is passed: the loop in
> af_alg_get_rsgl() just passes straight out and doesn't set areq->first_rs=
gl
> up.
>
> This isn't a problem on x86_64 using gcmaes_crypt_by_sg() because, as far
> as I can tell, that ignores req->dst and only uses req->src[*].
>
> [*] Is this a bug in aesni-intel_glue.c?
>
> The s390x oops looks something like:
>
>  Unable to handle kernel pointer dereference in virtual kernel address sp=
ace
>  Failing address: 0000000a00000000 TEID: 0000000a00000803
>  Fault in home space mode while using kernel ASCE.
>  AS:00000000a43a0007 R3:0000000000000024
>  Oops: 003b ilc:2 [#1] SMP
>  ...
>  Call Trace:
>   [<000003ff7fc3d47e>] gcm_walk_start+0x16/0x28 [aes_s390]
>   [<00000000a2a342f2>] crypto_aead_decrypt+0x9a/0xb8
>   [<00000000a2a60888>] aead_recvmsg+0x478/0x698
>   [<00000000a2e519a0>] sock_recvmsg+0x70/0xb0
>   [<00000000a2e51a56>] sock_read_iter+0x76/0xa0
>   [<00000000a273e066>] vfs_read+0x26e/0x2a8
>   [<00000000a273e8c4>] ksys_read+0xbc/0x100
>   [<00000000a311d808>] __do_syscall+0x1d0/0x1f8
>   [<00000000a312ff30>] system_call+0x70/0x98
>  Last Breaking-Event-Address:
>   [<000003ff7fc3e6b4>] gcm_aes_crypt+0x104/0xa68 [aes_s390]
>
> Fixes: c1abe6f570af ("crypto: af_alg: Use extract_iter_to_sg() to create =
scatterlists")
> Reported-by: Ondrej Mosn=C3=A1=C4=8Dek <omosnacek@gmail.com>
> Link: https://lore.kernel.org/r/CAAUqJDuRkHE8fPgZJGaKjUjd3QfGwzfumuJBmStP=
qBhubxyk_A@mail.gmail.com/
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Herbert Xu <herbert@gondor.apana.org.au>
> cc: Sven Schnelle <svens@linux.ibm.com>
> cc: Harald Freudenberger <freude@linux.vnet.ibm.com>
> cc: "David S. Miller" <davem@davemloft.net>
> cc: Paolo Abeni <pabeni@redhat.com>
> cc: linux-crypto@vger.kernel.org
> cc: linux-s390@vger.kernel.org
> cc: regressions@lists.linux.dev
> ---
>  crypto/af_alg.c |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> index 06b15b9f661c..9ee8575d3b1a 100644
> --- a/crypto/af_alg.c
> +++ b/crypto/af_alg.c
> @@ -1192,6 +1192,7 @@ struct af_alg_async_req *af_alg_alloc_areq(struct s=
ock *sk,
>=20=20
>  	areq->areqlen =3D areqlen;
>  	areq->sk =3D sk;
> +	areq->first_rsgl.sgl.sgt.sgl =3D areq->first_rsgl.sgl.sgl;
>  	areq->last_rsgl =3D NULL;
>  	INIT_LIST_HEAD(&areq->rsgl_list);
>  	areq->tsgl =3D NULL;

Just tested, with this fix the kernel no longer crashes. Thanks!

Tested-by: Sven Schnelle <svens@linux.ibm.com>