From: Jaco Kroon <jaco@uls.co.za>
Date: Thu, 21 Dec 2023 19:50:58 +0000 (+0200)
Subject: radius: Fix MPPE key decryption for the second-half of the key block (#463)
X-Git-Url: https://git.ozlabs.org/?p=ppp.git;a=commitdiff_plain;h=04f851936555d7157e2d518fa233778eb96d3f23

radius: Fix MPPE key decryption for the second-half of the key block (#463)

During he refactor in commit 4cb90c1 the key material used to decrypt
the second-half of the encrypted block was accidentally updated from:

MD5(radius_secret + crypt[0..15]); to:

MD5(radius_secret + crypt[0..15] + salt)

Which would obviously mismatch.

This also refactors back into what I believe to be a more readable block
with lower nesting and more comprehensive error reporting.

Closes: #453

Signed-off-by: Jaco Kroon <jaco@uls.co.za>
---

diff --git a/pppd/plugins/radius/radius.c b/pppd/plugins/radius/radius.c
index c73ca0b..e99bc75 100644
--- a/pppd/plugins/radius/radius.c
+++ b/pppd/plugins/radius/radius.c
@@ -897,80 +897,75 @@ radius_setmppekeys2(VALUE_PAIR *vp, REQUEST_INFO *req_info)
     memcpy(plain, crypt, 32);
 
     ctx = PPP_MD_CTX_new();
-    if (ctx) {
-
-        if (PPP_DigestInit(ctx, PPP_md5())) {
-
-            if (PPP_DigestUpdate(ctx, req_info->secret, strlen(req_info->secret))) {
-
-                if (PPP_DigestUpdate(ctx, req_info->request_vector, AUTH_VECTOR_LEN)) {
-
-                    if (PPP_DigestUpdate(ctx, salt, 2)) {
-
-                        buflen = sizeof(buf);
-                        if (PPP_DigestFinal(ctx, buf, &buflen)) {
-
-                            status = 1;
-                        }
-                    }
-                }
-            }
-        }
-
-        PPP_MD_CTX_free(ctx);
+    if (!ctx) {
+	error("RADIUS: Error creating PPP_MD_CTX for MS-MPPE-%s-Key attribute", type);
+	return -1;
     }
 
-    if (status) {
-
-        for (i = 0; i < 16; i++) {
-            plain[i] ^= buf[i];
-        }
+    buflen = sizeof(buf);
+    if (!PPP_DigestInit(ctx, PPP_md5())) {
+	error("RADIUS: Error setting hash algorithm to MD5 for MS-MPPE-%s-Key attribute", type);
+    } else if (!PPP_DigestUpdate(ctx, req_info->secret, strlen(req_info->secret))) {
+	error("RADIUS: Error mixing in radius secret for MS-MPPE-%s-Key attribute", type);
+    } else if (!PPP_DigestUpdate(ctx, req_info->request_vector, AUTH_VECTOR_LEN)) {
+	error("RADIUS: Error mixing in request vector for MS-MPPE-%s-Key attribute", type);
+    } else if (!PPP_DigestUpdate(ctx, salt, 2)) {
+	error("RADIUS: Error mixing in salt for MS-MPPE-%s-Key attribute", type);
+    } else if (!PPP_DigestFinal(ctx, buf, &buflen)) {
+	error("RADIUS: Error finalizing key buffer for MS-MPPE-%s-Key attribute", type);
+    } else {
+	status = 1;
+    }
 
-        if (plain[0] != 16) {
-            error("RADIUS: Incorrect key length (%d) for MS-MPPE-%s-Key attribute",
-                  (int) plain[0], type);
-            return -1;
-        }
+    PPP_MD_CTX_free(ctx);
 
-        status = 0;
-        ctx = PPP_MD_CTX_new();
-        if (ctx) {
-
-            if (PPP_DigestInit(ctx, PPP_md5())) {
+    if (!status)
+	return -1;
 
-                if (PPP_DigestUpdate(ctx, req_info->secret, strlen(req_info->secret))) {
+    for (i = 0; i < 16; i++) {
+	plain[i] ^= buf[i];
+    }
 
-                    if (PPP_DigestUpdate(ctx, crypt, 16)) {
+    if (plain[0] != 16) {
+	error("RADIUS: Incorrect key length (%d) for MS-MPPE-%s-Key attribute",
+		(int) plain[0], type);
+	return -1;
+    }
 
-                        if (PPP_DigestUpdate(ctx, salt, 2)) {
+    status = 0;
+    ctx = PPP_MD_CTX_new();
+    if (!ctx) {
+	error("RADIUS: Error creating PPP_MD_CTX for MS-MPPE-%s-Key(2) attribute", type);
+	return -1;
+    }
 
-                            buflen = sizeof(buf);
-                            if (PPP_DigestFinal(ctx, buf, &buflen)) {
+    buflen = sizeof(buf);
 
-                                status = 1;
-                            }
-                        }
-                    }
-                }
-            }
+    if (!PPP_DigestInit(ctx, PPP_md5())) {
+	error("RADIUS: Error setting hash algorithm to MD5 for MS-MPPE-%s-Key(2) attribute", type);
+    } else if (!PPP_DigestUpdate(ctx, req_info->secret, strlen(req_info->secret))) {
+	error("RADIUS: Error mixing in radius secret for MS-MPPE-%s-Key(2) attribute", type);
+    } else if (!PPP_DigestUpdate(ctx, crypt, 16)) {
+	error("RADIUS: Error mixing in crypt vector for MS-MPPE-%s-Key(2) attribute", type);
+    } else if (!PPP_DigestFinal(ctx, buf, &buflen)) {
+	error("RADIUS: Error finalizing key buffer for MS-MPPE-%s-Key(2) attribute", type);
+    } else {
+	status = 1;
+    }
 
-            PPP_MD_CTX_free(ctx);
-        }
+    PPP_MD_CTX_free(ctx);
 
-        if (status) {
+    if (!status)
+	return -1;
 
-            plain[16] ^= buf[0]; /* only need the first byte */
+    plain[16] ^= buf[0]; /* only need the first byte */
 
-            if (vp->attribute == PW_MS_MPPE_SEND_KEY) {
-                mppe_set_keys(plain + 1, NULL, 16);
-            } else {
-                mppe_set_keys(NULL, plain + 1, 16);
-            }
-            return 0;
-        }
+    if (vp->attribute == PW_MS_MPPE_SEND_KEY) {
+	mppe_set_keys(plain + 1, NULL, 16);
+    } else {
+	mppe_set_keys(NULL, plain + 1, 16);
     }
-
-    return -1;
+    return 0;
 }
 #endif /* PPP_WITH_MPPE */