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);
+}
+
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;
+ }
+
+ // 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);
+
+ 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
