libssh2: fix regression in KEX method validation (GH-1553)

Resolves: https://github.com/libssh2/libssh2/issues/1553

Regression caused by
https://github.com/libssh2/libssh2/commit/00e2a07e824db8798d94809156e9fb4e70a42f89

Backport fix
https://github.com/libssh2/libssh2/commit/4beed7245889ba149cc372f845d5969ce5103a5d

(From OE-Core rev: c348296ff0181921e8aa5a16d8d90db75f7b3e7c)

Signed-off-by: Vijay Anusuri <vanusuri@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 74 insertions, 0 deletions

diff --git a/meta/recipes-support/libssh2/libssh2/0001-Return-error-if-user-KEX-methods-are-invalid.patch b/meta/recipes-support/libssh2/libssh2/0001-Return-error-if-user-KEX-methods-are-invalid.patch
new file mode 100644
index 0000000000..9e7bb9a905
--- /dev/null
+++ b/meta/recipes-support/libssh2/libssh2/0001-Return-error-if-user-KEX-methods-are-invalid.patch
@@ -0,0 +1,73 @@
+From 4beed7245889ba149cc372f845d5969ce5103a5d Mon Sep 17 00:00:00 2001
+From: Will Cosgrove <will@panic.com>
+Date: Fri, 28 Feb 2025 09:32:30 -0800
+Subject: [PATCH] Return error if user KEX methods are invalid #1553 (#1554)
+
+Notes:
+Fixes #1553. Restores error case if user passes in invalid KEX method value to libssh2_session_method_pref.
+
+Credit:
+Amy Lin
+
+Upstream-Status: Backport [https://github.com/libssh2/libssh2/commit/4beed7245889ba149cc372f845d5969ce5103a5d]
+Signed-off-by: Vijay Anusuri <vanusuri@mvista.com>
+---
+ src/kex.c | 33 +++++++++++++++++++++------------
+ 1 file changed, 21 insertions(+), 12 deletions(-)
+
+diff --git a/src/kex.c b/src/kex.c
+index ebee54f987..bafda0e611 100644
+--- a/src/kex.c
++++ b/src/kex.c
+@@ -4196,23 +4196,11 @@ libssh2_session_method_pref(LIBSSH2_SESSION * session, int method_type,
+     char *tmpprefs = NULL;
+     size_t prefs_len = strlen(prefs);
+     const LIBSSH2_COMMON_METHOD **mlist;
+-    const char *kex_extensions = "ext-info-c,kex-strict-c-v00@openssh.com,";
+-    size_t kex_extensions_len = strlen(kex_extensions);
+ 
+     switch(method_type) {
+     case LIBSSH2_METHOD_KEX:
+         prefvar = &session->kex_prefs;
+         mlist = (const LIBSSH2_COMMON_METHOD **)libssh2_kex_methods;
+-        tmpprefs = LIBSSH2_ALLOC(session, kex_extensions_len + prefs_len + 1);
+-        if(!tmpprefs) {
+-            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
+-                                  "Error allocated space for kex method"
+-                                  " preferences");
+-        }
+-        memcpy(tmpprefs, kex_extensions, kex_extensions_len);
+-        memcpy(tmpprefs + kex_extensions_len, prefs, prefs_len + 1);
+-        prefs = tmpprefs;
+-        prefs_len = strlen(prefs);
+         break;
+ 
+     case LIBSSH2_METHOD_HOSTKEY:
+@@ -4314,6 +4302,27 @@ libssh2_session_method_pref(LIBSSH2_SESSION * session, int method_type,
+                               "supported");
+     }
+ 
++    /* add method kex extension to the start of the user list */
++    if(method_type == LIBSSH2_METHOD_KEX) {
++        const char *kex_extensions =
++                    "ext-info-c,kex-strict-c-v00@openssh.com,";
++        size_t kex_extensions_len = strlen(kex_extensions);
++        size_t tmp_len = kex_extensions_len + strlen(newprefs);
++        tmpprefs = LIBSSH2_ALLOC(session, tmp_len + 1);
++        if(!tmpprefs) {
++            return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
++                                  "Error allocated space for kex method"
++                                  " preferences");
++        }
++
++        memcpy(tmpprefs, kex_extensions, kex_extensions_len);
++        memcpy(tmpprefs + kex_extensions_len, newprefs, strlen(newprefs));
++        tmpprefs[tmp_len] = '\0';
++
++        LIBSSH2_FREE(session, newprefs);
++        newprefs = tmpprefs;
++    }
++
+     if(*prefvar) {
+         LIBSSH2_FREE(session, *prefvar);
+     }
diff --git a/meta/recipes-support/libssh2/libssh2_1.11.1.bb b/meta/recipes-support/libssh2/libssh2_1.11.1.bb
index fb63dea8b3..49da9698a3 100644
--- a/meta/recipes-support/libssh2/libssh2_1.11.1.bb
+++ b/meta/recipes-support/libssh2/libssh2_1.11.1.bb
@@ -9,6 +9,7 @@ LIC_FILES_CHKSUM = "file://COPYING;md5=2fbf8f834408079bf1fcbadb9814b1bc"
 
 SRC_URI = "http://www.libssh2.org/download/${BP}.tar.gz \
            file://run-ptest \
+           file://0001-Return-error-if-user-KEX-methods-are-invalid.patch \
            "
 
 SRC_URI[sha256sum] = "d9ec76cbe34db98eec3539fe2c899d26b0c837cb3eb466a56b0f109cabf658f7"