Subject: Re: [PATCH] crypto: Fix missing initialisation affecting gcm-aes-s390

From: Sven Schnelle <[email-masked]>
Date: Thu, 27 Jul 2023 07:55:18 +0200

David Howells <[email-masked]> writes:

>     
> Fix af_alg_alloc_areq() to initialise areq->first_rsgl.sgl.sgt.sgl to point
> 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_rsgl
> 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 space
>  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 Mosnáček <[email-masked]>
> Link: https://lore.kernel.org/r/[email-masked]/
> Signed-off-by: David Howells <[email-masked]>
> cc: Herbert Xu <[email-masked]>
> cc: Sven Schnelle <[email-masked]>
> cc: Harald Freudenberger <[email-masked]>
> cc: "David S. Miller" <[email-masked]>
> cc: Paolo Abeni <[email-masked]>
> cc: [email-masked]
> cc: [email-masked]
> cc: [email-masked]
> ---
>  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 sock *sk,
>  
>  	areq->areqlen = areqlen;
>  	areq->sk = sk;
> +	areq->first_rsgl.sgl.sgt.sgl = areq->first_rsgl.sgl.sgl;
>  	areq->last_rsgl = NULL;
>  	INIT_LIST_HEAD(&areq->rsgl_list);
>  	areq->tsgl = NULL;

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

Tested-by: Sven Schnelle <[email-masked]>