Add DebianBanner server configuration option

Setting this to "no" causes sshd to omit the Debian revision from its
initial protocol handshake, for those scared by package-versioning.patch.

Bug-Debian: http://bugs.debian.org/562048
Forwarded: not-needed
Last-Update: 2018-10-19

Patch-Name: debian-banner.patch

4 files changed, 18 insertions, 1 deletions

diff --git a/servconf.c b/servconf.c
index 6caf1db38..c5dd617ef 100644
--- a/servconf.c
+++ b/servconf.c
@@ -182,6 +182,7 @@ initialize_server_options(ServerOptions *options)
         options->fingerprint_hash = -1;
         options->disable_forwarding = -1;
         options->expose_userauth_info = -1;
+        options->debian_banner = -1;
 }
 
 /* Returns 1 if a string option is unset or set to "none" or 0 otherwise. */
@@ -417,6 +418,8 @@ fill_default_server_options(ServerOptions *options)
                 options->disable_forwarding = 0;
         if (options->expose_userauth_info == -1)
                 options->expose_userauth_info = 0;
+        if (options->debian_banner == -1)
+                options->debian_banner = 1;
 
         assemble_algorithms(options);
 
@@ -504,6 +507,7 @@ typedef enum {
         sStreamLocalBindMask, sStreamLocalBindUnlink,
         sAllowStreamLocalForwarding, sFingerprintHash, sDisableForwarding,
         sExposeAuthInfo, sRDomain,
+        sDebianBanner,
         sDeprecated, sIgnore, sUnsupported
 } ServerOpCodes;
 
@@ -661,6 +665,7 @@ static struct {
         { "exposeauthinfo", sExposeAuthInfo, SSHCFG_ALL },
         { "rdomain", sRDomain, SSHCFG_ALL },
         { "casignaturealgorithms", sCASignatureAlgorithms, SSHCFG_ALL },
+        { "debianbanner", sDebianBanner, SSHCFG_GLOBAL },
         { NULL, sBadOption, 0 }
 };
 
@@ -2173,6 +2178,10 @@ process_server_config_line(ServerOptions *options, char *line,
                         *charptr = xstrdup(arg);
                 break;
 
+        case sDebianBanner:
+                intptr = &options->debian_banner;
+                goto parse_flag;
+
         case sDeprecated:
         case sIgnore:
         case sUnsupported:
diff --git a/servconf.h b/servconf.h
index 3b76da816..4e3c54042 100644
--- a/servconf.h
+++ b/servconf.h
@@ -212,6 +212,8 @@ typedef struct {
         int     fingerprint_hash;
         int     expose_userauth_info;
         u_int64_t timing_secret;
+
+        int     debian_banner;
 }       ServerOptions;
 
 /* Information about the incoming connection as used by Match */
diff --git a/sshd.c b/sshd.c
index 9481272fc..d7e77d343 100644
--- a/sshd.c
+++ b/sshd.c
@@ -384,7 +384,8 @@ sshd_exchange_identification(struct ssh *ssh, int sock_in, int sock_out)
         char remote_version[256];       /* Must be at least as big as buf. */
 
         xasprintf(&server_version_string, "SSH-%d.%d-%.100s%s%s\r\n",
-            PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_RELEASE,
+            PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2,
+            options.debian_banner ? SSH_RELEASE : SSH_RELEASE_MINIMUM,
             *options.version_addendum == '\0' ? "" : " ",
             options.version_addendum);
 
diff --git a/sshd_config.5 b/sshd_config.5
index e7e55dd71..37e6be38f 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -543,6 +543,11 @@ or
 .Cm no .
 The default is
 .Cm yes .
+.It Cm DebianBanner
+Specifies whether the distribution-specified extra version suffix is
+included during initial protocol handshake.
+The default is
+.Cm yes .
 .It Cm DenyGroups
 This keyword can be followed by a list of group name patterns, separated
 by spaces.