linux-kernel - Re: [RFC][PATCH] almost certain bug in drivers/crypto/chelsio/chcr_algo.c:create_authenc

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Date:   Fri, 21 Feb 2020 10:47:01 +0530
From:   Ayush Sawal <ayush.sawal@...lsio.com>
To:     viro@...iv.linux.org.uk, Herbert Xu <herbert@...dor.apana.org.au>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        vinay.yadav@...lsio.com
Subject: Re: [RFC][PATCH] almost certain bug in
 drivers/crypto/chelsio/chcr_algo.c:create_authenc_wr()

On 2/15/2020 11:45 AM, Al Viro wrote:

>
>         kctx_len = (ntohl(KEY_CONTEXT_CTX_LEN_V(aeadctx->key_ctx_hdr)) 
> << 4)
>                 - sizeof(chcr_req->key_ctx);
> can't possibly be endian-safe.  Look: ->key_ctx_hdr is __be32.  And
> KEY_CONTEXT_CTX_LEN_V is "shift up by 24 bits".  On little-endian hosts it
> sees
>         b0 b1 b2 b3
> in memory, inteprets that into b0 + (b1 << 8) + (b2 << 16) + (b3 << 24),
> shifts up by 24, resulting in b0 << 24, does ntohl (byteswap on l-e),
> gets b0 and shifts that up by 4.  So we get b0 * 16 - sizeof(...).
>
> Sounds reasonable, but on b-e we get
> b3 + (b2 << 8) + (b1 << 16) + (b0 << 24), shift up by 24,
> yielding b3 << 24, do ntohl (no-op on b-e) and then shift up by 4.
> Resulting in b3 << 28 - sizeof(...), i.e. slightly under b3 * 256M.
>
> Then we increase it some more and pass to alloc_skb() as size.
> Somehow I doubt that we really want a quarter-gigabyte skb allocation
> here...
>
> Note that when you are building those values in
> #define  FILL_KEY_CTX_HDR(ck_size, mk_size, d_ck, opad, ctx_len) \
>                 htonl(KEY_CONTEXT_VALID_V(1) | \
>                       KEY_CONTEXT_CK_SIZE_V((ck_size)) | \
>                       KEY_CONTEXT_MK_SIZE_V(mk_size) | \
>                       KEY_CONTEXT_DUAL_CK_V((d_ck)) | \
>                       KEY_CONTEXT_OPAD_PRESENT_V((opad)) | \
>                       KEY_CONTEXT_SALT_PRESENT_V(1) | \
>                       KEY_CONTEXT_CTX_LEN_V((ctx_len)))
> ctx_len ends up in the first octet (i.e. b0 in the above), which
> matches the current behaviour on l-e.  If that's the intent, this
> thing should've been
>         kctx_len = (KEY_CONTEXT_CTX_LEN_G(ntohl(aeadctx->key_ctx_hdr)) 
> << 4)
>                 - sizeof(chcr_req->key_ctx);
> instead - fetch after ntohl() we get (b0 << 24) + (b1 << 16) + (b2 << 
> 8) + b3,
> shift it down by 24 (b0), resuling in b0 * 16 - sizeof(...) both on 
> l-e and
> on b-e.
>
> PS: when sparse warns you about endianness problems, it might be worth 
> checking
> if there really is something wrong.  And I don't mean "slap __force 
> cast on it"...
>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk 
> <mailto:viro@...iv.linux.org.uk>>
> ---
> diff -urN a/drivers/crypto/chelsio/chcr_algo.c 
> b/drivers/crypto/chelsio/chcr_algo.c
> --- a/drivers/crypto/chelsio/chcr_algo.c
> +++ b/drivers/crypto/chelsio/chcr_algo.c
> @@ -2351,7 +2351,7 @@ static struct sk_buff *create_authenc_wr(struct 
> aead_request *req,
>         snents = sg_nents_xlen(req->src, req->assoclen + req->cryptlen,
>                                CHCR_SRC_SG_SIZE, 0);
>         dst_size = get_space_for_phys_dsgl(dnents);
> -       kctx_len = (ntohl(KEY_CONTEXT_CTX_LEN_V(aeadctx->key_ctx_hdr)) 
> << 4)
> +       kctx_len = (KEY_CONTEXT_CTX_LEN_G(ntohl(aeadctx->key_ctx_hdr)) 
> << 4)
>                 - sizeof(chcr_req->key_ctx);
>         transhdr_len = CIPHER_TRANSHDR_SIZE(kctx_len, dst_size);
>         reqctx->imm = (transhdr_len + req->assoclen + req->cryptlen) <


This was a genuine bug, thanks a lot for pointing it out and providing
the fix.We are checking other sparse warns in our files, and soon we
will fix the warnings.

Thanks,
Ayush