From 4ac055f3ce8fdb5debb34df1370f4e87f7d8a179 Mon Sep 17 00:00:00 2001
From: Dan Fandrich <dan@coneharvesters.com>
Date: Tue, 21 Feb 2023 10:55:58 -0800
Subject: [PATCH] Fix AES-GCM when the last few bytes aren't received

---
 src/openssl.c   |  1 +
 src/transport.c | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/openssl.c b/src/openssl.c
index cec73c07..925efa85 100644
--- a/src/openssl.c
+++ b/src/openssl.c
@@ -492,6 +492,7 @@ _libssh2_cipher_crypt(_libssh2_cipher_ctx * ctx,
     (void) algo;
 
     assert(blocksize <= sizeof(buf));
+    assert(cryptlen >= 0);
 
     /* First block */
     if(IS_FIRST(firstlast)) {
diff --git a/src/transport.c b/src/transport.c
index aff323ec..018405a6 100644
--- a/src/transport.c
+++ b/src/transport.c
@@ -51,6 +51,9 @@
 #include "transport.h"
 #include "mac.h"
 
+#ifndef MAX
+#define MAX(x,y) ((x)>(y)?(x):(y))
+#endif
 #ifndef MIN
 #define MIN(x,y) ((x)<(y)?(x):(y))
 #endif
@@ -638,7 +641,8 @@ int _libssh2_transport_read(LIBSSH2_SESSION * session)
                amount to decrypt even more */
             if((p->data_num + numbytes) >= (p->total_num - skip)) {
                 /* decrypt the entire rest of the package */
-                numdecrypt = (p->total_num - skip) - p->data_num;
+                numdecrypt = MAX(0,
+                               (int)(p->total_num - skip) - (int)p->data_num);
                 firstlast = LAST_BLOCK;
             }
             else {
@@ -653,6 +657,13 @@ int _libssh2_transport_read(LIBSSH2_SESSION * session)
                        after it */
                     numbytes = 0;
                 }
+                if(CRYPT_FLAG_R(session, INTEGRATED_MAC)) {
+                    /* Make sure that we save enough bytes to make the last
+                     * block large enough to hold the entire integrated MAC */
+                    numdecrypt = MIN(numdecrypt, (int)
+                       (p->total_num - skip - blocksize - p->data_num));
+                    numbytes = 0;
+                }
                 firstlast = MIDDLE_BLOCK;
             }
 
@@ -661,6 +672,7 @@ int _libssh2_transport_read(LIBSSH2_SESSION * session)
             /* unencrypted data should not be decrypted at all */
             numdecrypt = 0;
         }
+        assert(numdecrypt >= 0);
 
         /* if there are bytes to decrypt, do that */
         if(numdecrypt > 0) {