2 files changed, 50 insertions, 9 deletions

diff --git a/readconf.c b/readconf.c
index ae1c31da0..5a1055bcb 100644
--- a/readconf.c
+++ b/readconf.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: readconf.c,v 1.285 2018/04/06 03:51:27 djm Exp $ */
+/* $OpenBSD: readconf.c,v 1.286 2018/04/06 13:02:39 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -684,6 +684,35 @@ match_cfg_line(Options *options, char **condition, struct passwd *pw,
         return result;
 }
 
+/* Remove environment variable by pattern */
+static void
+rm_env(Options *options, const char *arg, const char *filename, int linenum)
+{
+        int i, j;
+        char *cp;
+
+        /* Remove an environment variable */
+        for (i = 0; i < options->num_send_env; ) {
+                cp = xstrdup(options->send_env[i]);
+                if (!match_pattern(cp, arg + 1)) {
+                        free(cp);
+                        i++;
+                        continue;
+                }
+                debug3("%s line %d: removing environment %s",
+                    filename, linenum, cp);
+                free(cp);
+                free(options->send_env[i]);
+                options->send_env[i] = NULL;
+                for (j = i; j < options->num_send_env - 1; j++) {
+                        options->send_env[j] = options->send_env[j + 1];
+                        options->send_env[j + 1] = NULL;
+                }
+                options->num_send_env--;
+                /* NB. don't increment i */
+        }
+}
+
 /*
  * Returns the number of the token pointed to by cp or oBadOption.
  */
@@ -1359,11 +1388,18 @@ parse_keytypes:
                                     filename, linenum);
                         if (!*activep)
                                 continue;
-                        if (options->num_send_env >= MAX_SEND_ENV)
-                                fatal("%s line %d: too many send env.",
-                                    filename, linenum);
-                        options->send_env[options->num_send_env++] =
-                            xstrdup(arg);
+                        if (*arg == '-') {
+                                /* Removing an env var */
+                                rm_env(options, arg, filename, linenum);
+                                continue;
+                        } else {
+                                /* Adding an env var */
+                                if (options->num_send_env >= MAX_SEND_ENV)
+                                        fatal("%s line %d: too many send env.",
+                                            filename, linenum);
+                                options->send_env[options->num_send_env++] =
+                                    xstrdup(arg);
+                        }
                 }
                 break;
 
diff --git a/ssh_config.5 b/ssh_config.5
index 75a21b595..0e3c4db2e 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.270 2018/04/05 22:54:28 djm Exp $
-.Dd $Mdocdate: April 5 2018 $
+.\" $OpenBSD: ssh_config.5,v 1.271 2018/04/06 13:02:39 djm Exp $
+.Dd $Mdocdate: April 6 2018 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -1394,11 +1394,16 @@ Multiple environment variables may be separated by whitespace or spread
 across multiple
 .Cm SendEnv
 directives.
-The default is not to send any environment variables.
 .Pp
 See
 .Sx PATTERNS
 for more information on patterns.
+.Pp
+It is possible to clear previously-set
+.Cm SendEnv
+variable names by prefixing patterns with
+.Pa - .
+The default is not to send any environment variables.
 .It Cm ServerAliveCountMax
 Sets the number of server alive messages (see below) which may be
 sent without