Be more wary about OpenSSL not setting errno on error.

OpenSSL will sometimes return SSL_ERROR_SYSCALL without having set
errno; this is apparently a reflection of recv(2)'s habit of not
setting errno when reporting EOF.  Ensure that we treat such cases
the same as read EOF.  Previously, we'd frequently report them like
"could not accept SSL connection: Success" which is confusing, or
worse report them with an unrelated errno left over from some
previous syscall.

To fix, ensure that errno is zeroed immediately before the call,
and report its value only when it's not zero afterwards; otherwise
report EOF.

For consistency, I've applied the same coding pattern in libpq's
pqsecure_raw_read().  Bare recv(2) shouldn't really return -1 without
setting errno, but in case it does we might as well cope.

Per report from Andres Freund.  Back-patch to all supported versions.

Discussion: https://postgr.es/m/20231208181451.deqnflwxqoehhxpe@awork3.anarazel.de

diff --git a/src/backend/libpq/be-secure-openssl.c b/src/backend/libpq/be-secure-openssl.c
index 49dca0cda9fa808bfbe79afcd15d83e66ab4d547..4f1fd91ba4d6bb267133b31277347317d241328d 100644 (file)
--- a/src/backend/libpq/be-secure-openssl.c
+++ b/src/backend/libpq/be-secure-openssl.c
@@ -460,6 +460,7 @@ aloop:
     * per-thread error queue following another call to an OpenSSL I/O
     * routine.
     */
+   errno = 0;
    ERR_clear_error();
    r = SSL_accept(port->ssl);
    if (r <= 0)
@@ -496,7 +497,7 @@ aloop:
                                         WAIT_EVENT_SSL_OPEN_SERVER);
                goto aloop;
            case SSL_ERROR_SYSCALL:
-               if (r < 0)
+               if (r < 0 && errno != 0)
                    ereport(COMMERROR,
                            (errcode_for_socket_access(),
                             errmsg("could not accept SSL connection: %m")));
@@ -732,7 +733,7 @@ be_tls_read(Port *port, void *ptr, size_t len, int *waitfor)
            break;
        case SSL_ERROR_SYSCALL:
            /* leave it to caller to ereport the value of errno */
-           if (n != -1)
+           if (n != -1 || errno == 0)
            {
                errno = ECONNRESET;
                n = -1;
@@ -790,8 +791,14 @@ be_tls_write(Port *port, void *ptr, size_t len, int *waitfor)
            n = -1;
            break;
        case SSL_ERROR_SYSCALL:
-           /* leave it to caller to ereport the value of errno */
-           if (n != -1)
+
+           /*
+            * Leave it to caller to ereport the value of errno.  However, if
+            * errno is still zero then assume it's a read EOF situation, and
+            * report ECONNRESET.  (This seems possible because SSL_write can
+            * also do reads.)
+            */
+           if (n != -1 || errno == 0)
            {
                errno = ECONNRESET;
                n = -1;

diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index da5bb5fc5d3bfe37d83590308921cd64ae1beaf6..67535449a665fea28ac3ca555e1b1cfd1ce8e0aa 100644 (file)
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -936,6 +936,8 @@ pq_recvbuf(void)
    {
        int         r;
 
+       errno = 0;
+
        r = secure_read(MyProcPort, PqRecvBuffer + PqRecvLength,
                        PQ_RECV_BUFFER_SIZE - PqRecvLength);
 
@@ -948,10 +950,13 @@ pq_recvbuf(void)
             * Careful: an ereport() that tries to write to the client would
             * cause recursion to here, leading to stack overflow and core
             * dump!  This message must go *only* to the postmaster log.
+            *
+            * If errno is zero, assume it's EOF and let the caller complain.
             */
-           ereport(COMMERROR,
-                   (errcode_for_socket_access(),
-                    errmsg("could not receive data from client: %m")));
+           if (errno != 0)
+               ereport(COMMERROR,
+                       (errcode_for_socket_access(),
+                        errmsg("could not receive data from client: %m")));
            return EOF;
        }
        if (r == 0)
@@ -1028,6 +1033,8 @@ pq_getbyte_if_available(unsigned char *c)
    /* Put the socket into non-blocking mode */
    socket_set_nonblocking(true);
 
+   errno = 0;
+
    r = secure_read(MyProcPort, c, 1);
    if (r < 0)
    {
@@ -1044,10 +1051,13 @@ pq_getbyte_if_available(unsigned char *c)
             * Careful: an ereport() that tries to write to the client would
             * cause recursion to here, leading to stack overflow and core
             * dump!  This message must go *only* to the postmaster log.
+            *
+            * If errno is zero, assume it's EOF and let the caller complain.
             */
-           ereport(COMMERROR,
-                   (errcode_for_socket_access(),
-                    errmsg("could not receive data from client: %m")));
+           if (errno != 0)
+               ereport(COMMERROR,
+                       (errcode_for_socket_access(),
+                        errmsg("could not receive data from client: %m")));
            r = EOF;
        }
    }

diff --git a/src/interfaces/libpq/fe-secure-openssl.c b/src/interfaces/libpq/fe-secure-openssl.c
index 93cf70b0ed63eb6f7ba44b3b9c466b637f8613a7..25569e6d113e23b82d023722a7fdb558907e312d 100644 (file)
--- a/src/interfaces/libpq/fe-secure-openssl.c
+++ b/src/interfaces/libpq/fe-secure-openssl.c
@@ -207,7 +207,7 @@ rloop:
             */
            goto rloop;
        case SSL_ERROR_SYSCALL:
-           if (n < 0)
+           if (n < 0 && SOCK_ERRNO != 0)
            {
                result_errno = SOCK_ERRNO;
                if (result_errno == EPIPE ||
@@ -308,7 +308,13 @@ pgtls_write(PGconn *conn, const void *ptr, size_t len)
            n = 0;
            break;
        case SSL_ERROR_SYSCALL:
-           if (n < 0)
+
+           /*
+            * If errno is still zero then assume it's a read EOF situation,
+            * and report EOF.  (This seems possible because SSL_write can
+            * also do reads.)
+            */
+           if (n < 0 && SOCK_ERRNO != 0)
            {
                result_errno = SOCK_ERRNO;
                if (result_errno == EPIPE || result_errno == ECONNRESET)
@@ -1523,11 +1529,12 @@ open_client_SSL(PGconn *conn)
                     * was using the system CA pool. For other errors, log
                     * them using the normal SYSCALL logging.
                     */
-                   if (!save_errno && vcode == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY &&
+                   if (save_errno == 0 &&
+                       vcode == X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY &&
                        strcmp(conn->sslrootcert, "system") == 0)
                        libpq_append_conn_error(conn, "SSL error: certificate verify failed: %s",
                                                X509_verify_cert_error_string(vcode));
-                   else if (r == -1)
+                   else if (r == -1 && save_errno != 0)
                        libpq_append_conn_error(conn, "SSL SYSCALL error: %s",
                                                SOCK_STRERROR(save_errno, sebuf, sizeof(sebuf)));
                    else

diff --git a/src/interfaces/libpq/fe-secure.c b/src/interfaces/libpq/fe-secure.c
index 8069e381424ac67cf54dfa0654d54e4b2f2c8272..8444f19f087db1b08772554d03f04ac7b38777ba 100644 (file)
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -233,6 +233,8 @@ pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
    int         result_errno = 0;
    char        sebuf[PG_STRERROR_R_BUFLEN];
 
+   SOCK_ERRNO_SET(0);
+
    n = recv(conn->sock, ptr, len, 0);
 
    if (n < 0)
@@ -259,6 +261,11 @@ pqsecure_raw_read(PGconn *conn, void *ptr, size_t len)
                                        "\tbefore or while processing the request.");
                break;
 
+           case 0:
+               /* If errno didn't get set, treat it as regular EOF */
+               n = 0;
+               break;
+
            default:
                libpq_append_conn_error(conn, "could not receive data from server: %s",
                                        SOCK_STRERROR(result_errno,