tls: Fix improper revert in zerocopy_from_iter

The current code is problematic because the iov_iter is reverted and
never advanced in the non-error case. This patch skips the revert in the
non-error case. This patch also fixes the amount by which the iov_iter
is reverted. Currently, iov_iter is reverted by size, which can be
greater than the amount by which the iter was actually advanced.
Instead, only revert by the amount that the iter was advanced.

Fixes: 4718799 ("tls: Fix zerocopy_from_iter iov handling")
Signed-off-by: Doron Roberts-Kedes <doronrk@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_sw.c

@@ -263,7 +263,7 @@ static int zerocopy_from_iter(struct sock *sk, struct iov_iter *from,
 			      int length, int *pages_used,
 			      unsigned int *size_used,
 			      struct scatterlist *to, int to_max_pages,
-			      bool charge, bool revert)
+			      bool charge)
 {
 	struct page *pages[MAX_SKB_FRAGS];
 
@@ -312,10 +312,10 @@ static int zerocopy_from_iter(struct sock *sk, struct iov_iter *from,
 	}
 
 out:
+	if (rc)
+		iov_iter_revert(from, size - *size_used);
 	*size_used = size;
 	*pages_used = num_elem;
-	if (revert)
-		iov_iter_revert(from, size);
 
 	return rc;
 }
@@ -417,7 +417,7 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 				&ctx->sg_plaintext_size,
 				ctx->sg_plaintext_data,
 				ARRAY_SIZE(ctx->sg_plaintext_data),
-				true, false);
+				true);
 			if (ret)
 				goto fallback_to_reg_send;
 
@@ -428,8 +428,6 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 			continue;
 
 fallback_to_reg_send:
-			iov_iter_revert(&msg->msg_iter,
-					ctx->sg_plaintext_size - orig_size);
 			trim_sg(sk, ctx->sg_plaintext_data,
 				&ctx->sg_plaintext_num_elem,
 				&ctx->sg_plaintext_size,
@@ -834,7 +832,7 @@ int tls_sw_recvmsg(struct sock *sk,
 				err = zerocopy_from_iter(sk, &msg->msg_iter,
 							 to_copy, &pages,
 							 &chunk, &sgin[1],
-							 MAX_SKB_FRAGS,	false, true);
+							 MAX_SKB_FRAGS,	false);
 				if (err < 0)
 					goto fallback_to_reg_recv;