> -----Original Message-----
> From: Doron Roberts-Kedes [mailto:doro...@fb.com]
> Sent: Friday, August 3, 2018 6:00 AM
> To: David S . Miller <da...@davemloft.net>
> Cc: Dave Watson <davejwat...@fb.com>; Vakul Garg
> <vakul.g...@nxp.com>; Boris Pismenny <bor...@mellanox.com>; Aviad
> Yehezkel <avia...@mellanox.com>; netdev@vger.kernel.org; Doron
> Roberts-Kedes <doro...@fb.com>
> Subject: [PATCH net-next] net/tls: Calculate nsg for zerocopy path without
> skb_cow_data.
>
> decrypt_skb fails if the number of sg elements required to map is greater
> than MAX_SKB_FRAGS. As noted by Vakul Garg, nsg must always be
> calculated, but skb_cow_data adds unnecessary memcpy's for the zerocopy
> case.
>
> The new function skb_nsg calculates the number of scatterlist elements
> required to map the skb without the extra overhead of skb_cow_data. This
> function mimics the structure of skb_to_sgvec.
>
> Fixes: c46234ebb4d1 ("tls: RX path for ktls")
> Signed-off-by: Doron Roberts-Kedes <doro...@fb.com>
> ---
> net/tls/tls_sw.c | 89
> ++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 86 insertions(+), 3 deletions(-)
>
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c index
> ff3a6904a722..c62793601cfc 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -43,6 +43,76 @@
>
> #define MAX_IV_SIZE TLS_CIPHER_AES_GCM_128_IV_SIZE
>
> +static int __skb_nsg(struct sk_buff *skb, int offset, int len,
> + unsigned int recursion_level)
> +{
> + int start = skb_headlen(skb);
> + int i, copy = start - offset;
> + struct sk_buff *frag_iter;
> + int elt = 0;
> +
> + if (unlikely(recursion_level >= 24))
> + return -EMSGSIZE;
> +
> + if (copy > 0) {
> + if (copy > len)
> + copy = len;
> + elt++;
> + if ((len -= copy) == 0)
> + return elt;
> + offset += copy;
> + }
> +
> + for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> + int end;
> +
> + WARN_ON(start > offset + len);
> +
> + end = start + skb_frag_size(&skb_shinfo(skb)->frags[i]);
> + if ((copy = end - offset) > 0) {
> + if (copy > len)
> + copy = len;
> + elt++;
> + if (!(len -= copy))
> + return elt;
> + offset += copy;
> + }
> + start = end;
> + }
> +
> + skb_walk_frags(skb, frag_iter) {
> + int end, ret;
> +
> + WARN_ON(start > offset + len);
> +
> + end = start + frag_iter->len;
> + if ((copy = end - offset) > 0) {
> +
> + if (copy > len)
> + copy = len;
> + ret = __skb_nsg(frag_iter, offset - start, copy,
> + recursion_level + 1);
> + if (unlikely(ret < 0))
> + return ret;
> + elt += ret;
> + if ((len -= copy) == 0)
> + return elt;
> + offset += copy;
> + }
> + start = end;
> + }
> + BUG_ON(len);
> + return elt;
> +}
> +
> +/* Return the number of scatterlist elements required to completely map
> +the
> + * skb, or -EMSGSIZE if the recursion depth is exceeded.
> + */
> +static int skb_nsg(struct sk_buff *skb, int offset, int len) {
> + return __skb_nsg(skb, offset, len, 0); }
> +
These is generic function and useful elsewhere too.
Should the above two functions be exported by skbuff.c?
> static int tls_do_decryption(struct sock *sk,
> struct scatterlist *sgin,
> struct scatterlist *sgout,
> @@ -693,7 +763,7 @@ int decrypt_skb(struct sock *sk, struct sk_buff *skb,
> struct scatterlist sgin_arr[MAX_SKB_FRAGS + 2];
> struct scatterlist *sgin = &sgin_arr[0];
> struct strp_msg *rxm = strp_msg(skb);
> - int ret, nsg = ARRAY_SIZE(sgin_arr);
> + int ret, nsg;
> struct sk_buff *unused;
>
> ret = skb_copy_bits(skb, rxm->offset + TLS_HEADER_SIZE, @@ -
> 704,10 +774,23 @@ int decrypt_skb(struct sock *sk, struct sk_buff *skb,
>
> memcpy(iv, tls_ctx->rx.iv, TLS_CIPHER_AES_GCM_128_SALT_SIZE);
> if (!sgout) {
> - nsg = skb_cow_data(skb, 0, &unused) + 1;
> + nsg = skb_cow_data(skb, 0, &unused);
> + } else {
> + nsg = skb_nsg(skb,
> + rxm->offset + tls_ctx->rx.prepend_size,
> + rxm->full_len - tls_ctx->rx.prepend_size);
> + if (nsg <= 0)
> + return nsg;
Comparison should be (nsg < 1). TLS forbids '0' sized records.
> + }
> +
> + // We need one extra for ctx->rx_aad_ciphertext
> + nsg++;
> +
> + if (nsg > ARRAY_SIZE(sgin_arr))
> sgin = kmalloc_array(nsg, sizeof(*sgin), sk->sk_allocation);
Add check for kmalloc_array returnining NULL.
> +
> + if (!sgout)
> sgout = sgin;
> - }
>
> sg_init_table(sgin, nsg);
> sg_set_buf(&sgin[0], ctx->rx_aad_ciphertext, TLS_AAD_SPACE_SIZE);
> --
> 2.17.1
