upstream: backoff reading messages from active connections when the

input buffer is too full to read one, or if the output buffer is too full to
enqueue a response; feedback & ok dtucker@

OpenBSD-Commit-ID: df3c5b6d57c968975875de40d8955cbfed05a6c8

1 files changed, 18 insertions, 4 deletions

diff --git a/ssh-agent.c b/ssh-agent.c
index 6baebc313..d06ecfd98 100644
--- a/ssh-agent.c
+++ b/ssh-agent.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-agent.c,v 1.232 2018/11/09 02:57:58 djm Exp $ */
+/* $OpenBSD: ssh-agent.c,v 1.233 2019/01/22 22:58:50 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -96,6 +96,8 @@
 
 /* Maximum accepted message length */
 #define AGENT_MAX_LEN   (256*1024)
+/* Maximum bytes to read from client socket */
+#define AGENT_RBUF_LEN  (4096)
 
 typedef enum {
         AUTH_UNUSED,
@@ -839,7 +841,7 @@ handle_socket_read(u_int socknum)
 static int
 handle_conn_read(u_int socknum)
 {
-        char buf[1024];
+        char buf[AGENT_RBUF_LEN];
         ssize_t len;
         int r;
 
@@ -946,6 +948,7 @@ prepare_poll(struct pollfd **pfdp, size_t *npfdp, int *timeoutp, u_int maxfds)
         struct pollfd *pfd = *pfdp;
         size_t i, j, npfd = 0;
         time_t deadline;
+        int r;
 
         /* Count active sockets */
         for (i = 0; i < sockets_alloc; i++) {
@@ -983,8 +986,19 @@ prepare_poll(struct pollfd **pfdp, size_t *npfdp, int *timeoutp, u_int maxfds)
                 case AUTH_CONNECTION:
                         pfd[j].fd = sockets[i].fd;
                         pfd[j].revents = 0;
-                        /* XXX backoff when input buffer full */
-                        pfd[j].events = POLLIN;
+                        /*
+                         * Only prepare to read if we can handle a full-size
+                         * input read buffer and enqueue a max size reply..
+                         */
+                        if ((r = sshbuf_check_reserve(sockets[i].input,
+                            AGENT_RBUF_LEN)) == 0 &&
+                            (r = sshbuf_check_reserve(sockets[i].output,
+                             AGENT_MAX_LEN)) == 0)
+                                pfd[j].events = POLLIN;
+                        else if (r != SSH_ERR_NO_BUFFER_SPACE) {
+                                fatal("%s: buffer error: %s",
+                                    __func__, ssh_err(r));
+                        }
                         if (sshbuf_len(sockets[i].output) > 0)
                                 pfd[j].events |= POLLOUT;
                         j++;