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From 90c1c8771b61dd3ee0eacb4e1cfac404dc42f4b0 Mon Sep 17 00:00:00 2001
From: Kees Cook <kees@debian.org>
Date: Sun, 9 Feb 2014 16:10:06 +0000
Subject: 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: 2020-06-07
Patch-Name: debian-banner.patch
---
kex.c | 5 +++--
kex.h | 2 +-
servconf.c | 9 +++++++++
servconf.h | 2 ++
sshconnect.c | 2 +-
sshd.c | 2 +-
sshd_config.5 | 5 +++++
7 files changed, 22 insertions(+), 5 deletions(-)
diff --git a/kex.c b/kex.c
index 0e64bf760..aa5acaac3 100644
--- a/kex.c
+++ b/kex.c
@@ -1225,7 +1225,7 @@ send_error(struct ssh *ssh, char *msg)
*/
int
kex_exchange_identification(struct ssh *ssh, int timeout_ms,
- const char *version_addendum)
+ int debian_banner, const char *version_addendum)
{
int remote_major, remote_minor, mismatch, oerrno = 0;
size_t len, i, n;
@@ -1243,7 +1243,8 @@ kex_exchange_identification(struct ssh *ssh, int timeout_ms,
if (version_addendum != NULL && *version_addendum == '\0')
version_addendum = NULL;
if ((r = sshbuf_putf(our_version, "SSH-%d.%d-%.100s%s%s\r\n",
- PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_RELEASE,
+ PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2,
+ debian_banner ? SSH_RELEASE : SSH_RELEASE_MINIMUM,
version_addendum == NULL ? "" : " ",
version_addendum == NULL ? "" : version_addendum)) != 0) {
oerrno = errno;
diff --git a/kex.h b/kex.h
index fe7141414..938dca03b 100644
--- a/kex.h
+++ b/kex.h
@@ -194,7 +194,7 @@ char *kex_names_cat(const char *, const char *);
int kex_assemble_names(char **, const char *, const char *);
int kex_gss_names_valid(const char *);
-int kex_exchange_identification(struct ssh *, int, const char *);
+int kex_exchange_identification(struct ssh *, int, int, const char *);
struct kex *kex_new(void);
int kex_ready(struct ssh *, char *[PROPOSAL_MAX]);
diff --git a/servconf.c b/servconf.c
index ff5b9436c..cf4e52f3b 100644
--- a/servconf.c
+++ b/servconf.c
@@ -194,6 +194,7 @@ 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. */
@@ -468,6 +469,8 @@ fill_default_server_options(ServerOptions *options)
options->expose_userauth_info = 0;
if (options->sk_provider == NULL)
options->sk_provider = xstrdup("internal");
+ if (options->debian_banner == -1)
+ options->debian_banner = 1;
assemble_algorithms(options);
@@ -556,6 +559,7 @@ typedef enum {
sStreamLocalBindMask, sStreamLocalBindUnlink,
sAllowStreamLocalForwarding, sFingerprintHash, sDisableForwarding,
sExposeAuthInfo, sRDomain, sPubkeyAuthOptions, sSecurityKeyProvider,
+ sDebianBanner,
sDeprecated, sIgnore, sUnsupported
} ServerOpCodes;
@@ -719,6 +723,7 @@ static struct {
{ "rdomain", sRDomain, SSHCFG_ALL },
{ "casignaturealgorithms", sCASignatureAlgorithms, SSHCFG_ALL },
{ "securitykeyprovider", sSecurityKeyProvider, SSHCFG_GLOBAL },
+ { "debianbanner", sDebianBanner, SSHCFG_GLOBAL },
{ NULL, sBadOption, 0 }
};
@@ -2393,6 +2398,10 @@ process_server_config_line_depth(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 253cad97e..5a2b60512 100644
--- a/servconf.h
+++ b/servconf.h
@@ -226,6 +226,8 @@ typedef struct {
int expose_userauth_info;
u_int64_t timing_secret;
char *sk_provider;
+
+ int debian_banner;
} ServerOptions;
/* Information about the incoming connection as used by Match */
diff --git a/sshconnect.c b/sshconnect.c
index f20d3e792..1e5b8ea5a 100644
--- a/sshconnect.c
+++ b/sshconnect.c
@@ -1293,7 +1293,7 @@ ssh_login(struct ssh *ssh, Sensitive *sensitive, const char *orighost,
lowercase(host);
/* Exchange protocol version identification strings with the server. */
- if ((r = kex_exchange_identification(ssh, timeout_ms, NULL)) != 0)
+ if ((r = kex_exchange_identification(ssh, timeout_ms, 1, NULL)) != 0)
sshpkt_fatal(ssh, r, "banner exchange");
/* Put the connection into non-blocking mode. */
diff --git a/sshd.c b/sshd.c
index e8b332ca4..baee13506 100644
--- a/sshd.c
+++ b/sshd.c
@@ -2181,7 +2181,7 @@ main(int ac, char **av)
if (!debug_flag)
alarm(options.login_grace_time);
- if ((r = kex_exchange_identification(ssh, -1,
+ if ((r = kex_exchange_identification(ssh, -1, options.debian_banner,
options.version_addendum)) != 0)
sshpkt_fatal(ssh, r, "banner exchange");
diff --git a/sshd_config.5 b/sshd_config.5
index 9f093be1f..753ceda10 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -540,6 +540,11 @@ 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.
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