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 6b8125695a31719fa5c9ffdfb09982ca59013f34..22e3dc5a8134a02cf16068eced432eb14716cde9 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 2802efc63fcdbaa895f92826a1d7ff6e751f57ed..0084a9bf132fa3a2e9e06b30a5acc62532c0791b 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 e669bdbf1d2dacb72d85e484b9a6ff0712864659..2b221e7d15150006a28edb0c598a6b5674346c0f 100644 (file)
--- a/src/interfaces/libpq/fe-secure-openssl.c
+++ b/src/interfaces/libpq/fe-secure-openssl.c
@@ -200,7 +200,7 @@ rloop:
             */
            goto rloop;
        case SSL_ERROR_SYSCALL:
-           if (n < 0)
+           if (n < 0 && SOCK_ERRNO != 0)
            {
                result_errno = SOCK_ERRNO;
                if (result_errno == EPIPE ||
@@ -301,7 +301,13 @@ 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)
@@ -1510,11 +1516,12 @@ 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 bd72a87bbbae67307cdaf06dccad59046c88d8c4..b2430362a9010e60dee70d1662e4f2cdf23d4f70 100644 (file)
--- a/src/interfaces/libpq/fe-secure.c
+++ b/src/interfaces/libpq/fe-secure.c
@@ -211,6 +211,8 @@ 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)
@@ -237,6 +239,11 @@ 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,