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

[Ondrej Mosnáček]

On Thu, Jul 27, 2023 at 7:55 AM Sven Schnelle <svens@xxxxxxxxxxxxx> wrote:
>
> David Howells <dhowells@xxxxxxxxxx> 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 <omosnacek@xxxxxxxxx>
> > Link: https://lore.kernel.org/r/CAAUqJDuRkHE8fPgZJGaKjUjd3QfGwzfumuJBmStPqBhubxyk_A@xxxxxxxxxxxxxx/
> > Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> > cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
> > cc: Harald Freudenberger <freude@xxxxxxxxxxxxxxxxxx>
> > cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> > cc: linux-crypto@xxxxxxxxxxxxxxx
> > cc: linux-s390@xxxxxxxxxxxxxxx
> > cc: regressions@xxxxxxxxxxxxxxx
> > ---
> >  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 <svens@xxxxxxxxxxxxx>

Same here. Thanks for the fix!

Tested-by: Ondrej Mosnáček <omosnacek@xxxxxxxxx>