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sendf: change Curl_read_plain to wrap Curl_recv_plain

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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
This commit is contained in:
Jay Satiro 2022-11-14 03:30:30 -05:00
parent 856b133f5d
commit 12e1def51a
5 changed files with 59 additions and 40 deletions
Download patch file Download diff file Expand all files Collapse all files

62
lib/sendf.c
View file

@ -338,6 +338,7 @@ CURLcode Curl_write(struct Curl_easy *data,
}
}
/* Curl_send_plain sends raw data without a size restriction on 'len'. */
ssize_t Curl_send_plain(struct Curl_easy *data, int num,
const void *mem, size_t len, CURLcode *code)
{
@ -403,7 +404,11 @@ ssize_t Curl_send_plain(struct Curl_easy *data, int num,
/*
* Curl_write_plain() is an internal write function that sends data to the
* server using plain sockets only. Otherwise meant to have the exact same
* proto as Curl_write()
* proto as Curl_write().
*
* This function wraps Curl_send_plain(). The only difference should be the
* prototype. 'sockfd' must be one of the connection's two main sockets and
* the value of 'len' must not be changed.
*/
CURLcode Curl_write_plain(struct Curl_easy *data,
curl_socket_t sockfd,
@ -415,6 +420,12 @@ CURLcode Curl_write_plain(struct Curl_easy *data,
struct connectdata *conn = data->conn;
int num;
DEBUGASSERT(conn);
DEBUGASSERT(sockfd == conn->sock[FIRSTSOCKET] ||
sockfd == conn->sock[SECONDARYSOCKET]);
if(sockfd != conn->sock[FIRSTSOCKET] &&
sockfd != conn->sock[SECONDARYSOCKET])
return CURLE_BAD_FUNCTION_ARGUMENT;
num = (sockfd == conn->sock[SECONDARYSOCKET]);
*written = Curl_send_plain(data, num, mem, len, &result);
@ -422,6 +433,7 @@ CURLcode Curl_write_plain(struct Curl_easy *data,
return result;
}
/* Curl_recv_plain receives raw data without a size restriction on 'len'. */
ssize_t Curl_recv_plain(struct Curl_easy *data, int num, char *buf,
size_t len, CURLcode *code)
{
@ -663,30 +675,36 @@ CURLcode Curl_client_write(struct Curl_easy *data,
return chop_write(data, type, ptr, len);
}
CURLcode Curl_read_plain(curl_socket_t sockfd,
char *buf,
size_t bytesfromsocket,
ssize_t *n)
/*
* Curl_read_plain() is an internal read function that reads data from the
* server using plain sockets only. Otherwise meant to have the exact same
* proto as Curl_read().
*
* This function wraps Curl_recv_plain(). The only difference should be the
* prototype. 'sockfd' must be one of the connection's two main sockets and
* the value of 'sizerequested' must not be changed.
*/
CURLcode Curl_read_plain(struct Curl_easy *data, /* transfer */
curl_socket_t sockfd, /* read from this socket */
char *buf, /* store read data here */
size_t sizerequested, /* max amount to read */
ssize_t *n) /* amount bytes read */
{
ssize_t nread = sread(sockfd, buf, bytesfromsocket);
CURLcode result;
struct connectdata *conn = data->conn;
int num;
DEBUGASSERT(conn);
DEBUGASSERT(sockfd == conn->sock[FIRSTSOCKET] ||
sockfd == conn->sock[SECONDARYSOCKET]);
if(sockfd != conn->sock[FIRSTSOCKET] &&
sockfd != conn->sock[SECONDARYSOCKET])
return CURLE_BAD_FUNCTION_ARGUMENT;
if(-1 == nread) {
const int err = SOCKERRNO;
const bool return_error =
#ifdef USE_WINSOCK
WSAEWOULDBLOCK == err
#else
EWOULDBLOCK == err || EAGAIN == err || EINTR == err
#endif
;
*n = 0; /* no data returned */
if(return_error)
return CURLE_AGAIN;
return CURLE_RECV_ERROR;
}
num = (sockfd == conn->sock[SECONDARYSOCKET]);
*n = nread;
return CURLE_OK;
*n = Curl_recv_plain(data, num, buf, sizerequested, &result);
return result;
}
/*