[Buildroot] [PATCH 1/1] package/libssh2: fix CVE-2019-17498

* [Buildroot] [PATCH 1/1] package/libssh2: fix CVE-2019-17498
@ 2020-02-29 11:31 Fabrice Fontaine
  2020-02-29 16:32 ` Yann E. MORIN
  2020-03-14 17:32 ` Peter Korsgaard
  0 siblings, 2 replies; 3+ messages in thread
From: Fabrice Fontaine @ 2020-02-29 11:31 UTC (permalink / raw)
  To: buildroot

In libssh2 v1.9.0 and earlier versions, the SSH_MSG_DISCONNECT logic in
packet.c has an integer overflow in a bounds check, enabling an attacker
to specify an arbitrary (out-of-bounds) offset for a subsequent memory
read. A crafted SSH server may be able to disclose sensitive information
or cause a denial of service condition on the client system when a user
connects to the server.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
---
 ...003-packet-c-improve-message-parsing.patch | 127 ++++++++++++++++++
 package/libssh2/libssh2.mk                    |   3 +
 2 files changed, 130 insertions(+)
 create mode 100644 package/libssh2/0003-packet-c-improve-message-parsing.patch

diff --git a/package/libssh2/0003-packet-c-improve-message-parsing.patch b/package/libssh2/0003-packet-c-improve-message-parsing.patch
new file mode 100644
index 0000000000..2b73520021
--- /dev/null
+++ b/package/libssh2/0003-packet-c-improve-message-parsing.patch
@@ -0,0 +1,127 @@
+From dedcbd106f8e52d5586b0205bc7677e4c9868f9c Mon Sep 17 00:00:00 2001
+From: Will Cosgrove <will@panic.com>
+Date: Fri, 30 Aug 2019 09:57:38 -0700
+Subject: [PATCH] packet.c: improve message parsing (#402)
+
+* packet.c: improve parsing of packets
+
+file: packet.c
+
+notes:
+Use _libssh2_get_string API in SSH_MSG_DEBUG/SSH_MSG_DISCONNECT. Additional uint32 bounds check in SSH_MSG_GLOBAL_REQUEST.
+[Retrieved from:
+https://github.com/libssh2/libssh2/commit/dedcbd106f8e52d5586b0205bc7677e4c9868f9c]
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ src/packet.c | 68 ++++++++++++++++++++++------------------------------
+ 1 file changed, 29 insertions(+), 39 deletions(-)
+
+diff --git a/src/packet.c b/src/packet.c
+index 38ab6294..2e01bfc5 100644
+--- a/src/packet.c
++++ b/src/packet.c
+@@ -419,8 +419,8 @@ _libssh2_packet_add(LIBSSH2_SESSION * session, unsigned char *data,
+                     size_t datalen, int macstate)
+ {
+     int rc = 0;
+-    char *message = NULL;
+-    char *language = NULL;
++    unsigned char *message = NULL;
++    unsigned char *language = NULL;
+     size_t message_len = 0;
+     size_t language_len = 0;
+     LIBSSH2_CHANNEL *channelp = NULL;
+@@ -472,33 +472,23 @@ _libssh2_packet_add(LIBSSH2_SESSION * session, unsigned char *data,
+ 
+         case SSH_MSG_DISCONNECT:
+             if(datalen >= 5) {
+-                size_t reason = _libssh2_ntohu32(data + 1);
++                uint32_t reason = 0;
++                struct string_buf buf;
++                buf.data = (unsigned char *)data;
++                buf.dataptr = buf.data;
++                buf.len = datalen;
++                buf.dataptr++; /* advance past type */
+ 
+-                if(datalen >= 9) {
+-                    message_len = _libssh2_ntohu32(data + 5);
++                _libssh2_get_u32(&buf, &reason);
++                _libssh2_get_string(&buf, &message, &message_len);
++                _libssh2_get_string(&buf, &language, &language_len);
+ 
+-                    if(message_len < datalen-13) {
+-                        /* 9 = packet_type(1) + reason(4) + message_len(4) */
+-                        message = (char *) data + 9;
+-
+-                        language_len =
+-                            _libssh2_ntohu32(data + 9 + message_len);
+-                        language = (char *) data + 9 + message_len + 4;
+-
+-                        if(language_len > (datalen-13-message_len)) {
+-                            /* bad input, clear info */
+-                            language = message = NULL;
+-                            language_len = message_len = 0;
+-                        }
+-                    }
+-                    else
+-                        /* bad size, clear it */
+-                        message_len = 0;
+-                }
+                 if(session->ssh_msg_disconnect) {
+-                    LIBSSH2_DISCONNECT(session, reason, message,
+-                                       message_len, language, language_len);
++                    LIBSSH2_DISCONNECT(session, reason, (const char *)message,
++                                       message_len, (const char *)language,
++                                       language_len);
+                 }
++
+                 _libssh2_debug(session, LIBSSH2_TRACE_TRANS,
+                                "Disconnect(%d): %s(%s)", reason,
+                                message, language);
+@@ -539,24 +529,24 @@ _libssh2_packet_add(LIBSSH2_SESSION * session, unsigned char *data,
+                 int always_display = data[1];
+ 
+                 if(datalen >= 6) {
+-                    message_len = _libssh2_ntohu32(data + 2);
+-
+-                    if(message_len <= (datalen - 10)) {
+-                        /* 6 = packet_type(1) + display(1) + message_len(4) */
+-                        message = (char *) data + 6;
+-                        language_len = _libssh2_ntohu32(data + 6 +
+-                                                        message_len);
+-
+-                        if(language_len <= (datalen - 10 - message_len))
+-                            language = (char *) data + 10 + message_len;
+-                    }
++                    struct string_buf buf;
++                    buf.data = (unsigned char *)data;
++                    buf.dataptr = buf.data;
++                    buf.len = datalen;
++                    buf.dataptr += 2; /* advance past type & always display */
++
++                    _libssh2_get_string(&buf, &message, &message_len);
++                    _libssh2_get_string(&buf, &language, &language_len);
+                 }
+ 
+                 if(session->ssh_msg_debug) {
+-                    LIBSSH2_DEBUG(session, always_display, message,
+-                                  message_len, language, language_len);
++                    LIBSSH2_DEBUG(session, always_display,
++                                  (const char *)message,
++                                  message_len, (const char *)language,
++                                  language_len);
+                 }
+             }
++
+             /*
+              * _libssh2_debug will actually truncate this for us so
+              * that it's not an inordinate about of data
+@@ -579,7 +569,7 @@ _libssh2_packet_add(LIBSSH2_SESSION * session, unsigned char *data,
+                 uint32_t len = 0;
+                 unsigned char want_reply = 0;
+                 len = _libssh2_ntohu32(data + 1);
+-                if(datalen >= (6 + len)) {
++                if((len <= (UINT_MAX - 6)) && (datalen >= (6 + len))) {
+                     want_reply = data[5 + len];
+                     _libssh2_debug(session,
+                                    LIBSSH2_TRACE_CONN,
diff --git a/package/libssh2/libssh2.mk b/package/libssh2/libssh2.mk
index bd8517dac4..3819c1aa31 100644
--- a/package/libssh2/libssh2.mk
+++ b/package/libssh2/libssh2.mk
@@ -11,6 +11,9 @@ LIBSSH2_LICENSE_FILES = COPYING
 LIBSSH2_INSTALL_STAGING = YES
 LIBSSH2_CONF_OPTS = --disable-examples-build
 
+# 0003-packet-c-improve-message-parsing.patch
+LIBSSH2_IGNORE_CVES += CVE-2019-17498
+
 # building from a git clone
 LIBSSH2_AUTORECONF = YES
 
-- 
2.25.0

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