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From 0a938d856d024bfff79fac63e65df382ffa444a4 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: 2019-06-05
Patch-Name: debian-banner.patch
---
kex.c | 5 +++--
kex.h | 2 +-
servconf.c | 9 +++++++++
servconf.h | 2 ++
sshconnect.c | 2 +-
sshd.c | 3 ++-
sshd_config.5 | 5 +++++
7 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/kex.c b/kex.c
index be354206d..bbb7a2340 100644
--- a/kex.c
+++ b/kex.c
@@ -1168,7 +1168,7 @@ 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;
size_t len, i, n;
@@ -1186,7 +1186,8 @@ 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) {
error("%s: sshbuf_putf: %s", __func__, ssh_err(r));
diff --git a/kex.h b/kex.h
index 2d5f1d4ed..39f67bbc1 100644
--- a/kex.h
+++ b/kex.h
@@ -195,7 +195,7 @@ 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 c01e0690e..8d2bced52 100644
--- a/servconf.c
+++ b/servconf.c
@@ -184,6 +184,7 @@ 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. */
@@ -437,6 +438,8 @@ 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);
@@ -523,6 +526,7 @@ typedef enum {
sStreamLocalBindMask, sStreamLocalBindUnlink,
sAllowStreamLocalForwarding, sFingerprintHash, sDisableForwarding,
sExposeAuthInfo, sRDomain,
+ sDebianBanner,
sDeprecated, sIgnore, sUnsupported
} ServerOpCodes;
@@ -682,6 +686,7 @@ static struct {
{ "exposeauthinfo", sExposeAuthInfo, SSHCFG_ALL },
{ "rdomain", sRDomain, SSHCFG_ALL },
{ "casignaturealgorithms", sCASignatureAlgorithms, SSHCFG_ALL },
+ { "debianbanner", sDebianBanner, SSHCFG_GLOBAL },
{ NULL, sBadOption, 0 }
};
@@ -2211,6 +2216,10 @@ 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 a476d5220..986093ffa 100644
--- a/servconf.h
+++ b/servconf.h
@@ -214,6 +214,8 @@ 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/sshconnect.c b/sshconnect.c
index 0b6f6af4b..1183ffe0e 100644
--- a/sshconnect.c
+++ b/sshconnect.c
@@ -1287,7 +1287,7 @@ ssh_login(struct ssh *ssh, Sensitive *sensitive, const char *orighost,
lowercase(host);
/* Exchange protocol version identification strings with the server. */
- if (kex_exchange_identification(ssh, timeout_ms, NULL) != 0)
+ if (kex_exchange_identification(ssh, timeout_ms, 1, NULL) != 0)
cleanup_exit(255); /* error already logged */
/* Put the connection into non-blocking mode. */
diff --git a/sshd.c b/sshd.c
index e3e96426e..1e7ece588 100644
--- a/sshd.c
+++ b/sshd.c
@@ -2160,7 +2160,8 @@ main(int ac, char **av)
if (!debug_flag)
alarm(options.login_grace_time);
- if (kex_exchange_identification(ssh, -1, options.version_addendum) != 0)
+ if (kex_exchange_identification(ssh, -1, options.debian_banner,
+ options.version_addendum) != 0)
cleanup_exit(255); /* error already logged */
ssh_packet_set_nonblocking(ssh);
diff --git a/sshd_config.5 b/sshd_config.5
index 2ef671d1b..addea54a0 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.
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