sendf: change Curl_read_plain to wrap Curl_recv_plain

Prior to this change Curl_read_plain would attempt to read the
socket directly. On Windows that's a problem because recv data may be
cached by libcurl and that data is only drained using Curl_recv_plain.

Rather than rewrite Curl_read_plain to handle cached recv data, I
changed it to wrap Curl_recv_plain, in much the same way that
Curl_write_plain already wraps Curl_send_plain.

Curl_read_plain -> Curl_recv_plain
Curl_write_plain -> Curl_send_plain

This fixes a bug in the schannel backend where decryption of arbitrary
TLS records fails because cached recv data is never drained. We send
data (TLS records formed by Schannel) using Curl_write_plain, which
calls Curl_send_plain, and that may do a recv-before-send
("pre-receive") to cache received data. The code calls Curl_read_plain
to read data (TLS records from the server), which prior to this change
did not call Curl_recv_plain and therefore cached recv data wasn't
retrieved, resulting in malformed TLS records and decryption failure
(SEC_E_DECRYPT_FAILURE).

The bug has only been observed during Schannel TLS 1.3 handshakes. Refer
to the issue and PR for more information.

Ref: https://github.com/curl/curl/issues/9431#issuecomment-1312420361

Assisted-by: Joel Depooter
Reported-by: Egor Pugin

Fixes https://github.com/curl/curl/issues/9431
Closes https://github.com/curl/curl/pull/9904

1 files changed, 6 insertions, 6 deletions

diff --git a/lib/socks.c b/lib/socks.c
index 40cd13e0a..e1f6dbbb2 100644
--- a/lib/socks.c
+++ b/lib/socks.c
@@ -112,7 +112,7 @@ int Curl_blockread_all(struct Curl_easy *data,   /* transfer */
       result = ~CURLE_OK;
       break;
     }
-    result = Curl_read_plain(sockfd, buf, buffersize, &nread);
+    result = Curl_read_plain(data, sockfd, buf, buffersize, &nread);
     if(CURLE_AGAIN == result)
       continue;
     if(result)
@@ -396,7 +396,7 @@ static CURLproxycode do_SOCKS4(struct Curl_cfilter *cf,
     /* FALLTHROUGH */
   case CONNECT_SOCKS_READ:
     /* Receive response */
-    result = Curl_read_plain(sockfd, (char *)sx->outp,
+    result = Curl_read_plain(data, sockfd, (char *)sx->outp,
                              sx->outstanding, &actualread);
     if(result && (CURLE_AGAIN != result)) {
       failf(data, "SOCKS4: Failed receiving connect request ack: %s",
@@ -599,7 +599,7 @@ static CURLproxycode do_SOCKS5(struct Curl_cfilter *cf,
     sx->outp = socksreq; /* store it here */
     /* FALLTHROUGH */
   case CONNECT_SOCKS_READ:
-    result = Curl_read_plain(sockfd, (char *)sx->outp,
+    result = Curl_read_plain(data, sockfd, (char *)sx->outp,
                              sx->outstanding, &actualread);
     if(result && (CURLE_AGAIN != result)) {
       failf(data, "Unable to receive initial SOCKS5 response.");
@@ -729,7 +729,7 @@ static CURLproxycode do_SOCKS5(struct Curl_cfilter *cf,
     sxstate(sx, data, CONNECT_AUTH_READ);
     /* FALLTHROUGH */
   case CONNECT_AUTH_READ:
-    result = Curl_read_plain(sockfd, (char *)sx->outp,
+    result = Curl_read_plain(data, sockfd, (char *)sx->outp,
                              sx->outstanding, &actualread);
     if(result && (CURLE_AGAIN != result)) {
       failf(data, "Unable to receive SOCKS5 sub-negotiation response.");
@@ -931,7 +931,7 @@ static CURLproxycode do_SOCKS5(struct Curl_cfilter *cf,
     sxstate(sx, data, CONNECT_REQ_READ);
     /* FALLTHROUGH */
   case CONNECT_REQ_READ:
-    result = Curl_read_plain(sockfd, (char *)sx->outp,
+    result = Curl_read_plain(data, sockfd, (char *)sx->outp,
                              sx->outstanding, &actualread);
     if(result && (CURLE_AGAIN != result)) {
       failf(data, "Failed to receive SOCKS5 connect request ack.");
@@ -1030,7 +1030,7 @@ static CURLproxycode do_SOCKS5(struct Curl_cfilter *cf,
 #endif
     /* FALLTHROUGH */
   case CONNECT_REQ_READ_MORE:
-    result = Curl_read_plain(sockfd, (char *)sx->outp,
+    result = Curl_read_plain(data, sockfd, (char *)sx->outp,
                              sx->outstanding, &actualread);
     if(result && (CURLE_AGAIN != result)) {
       failf(data, "Failed to receive SOCKS5 connect request ack.");