Don't overflow the output length in EVP_CipherUpdate calls

CVE-2021-23840 Reviewed-by: Paul Dale <pauli@openssl.org>
openssl · Feb 16, 2021 · 6a51b9e · 6a51b9e
1 parent 481a88f
commit 6a51b9e
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Showing 4 changed files with 35 additions and 6 deletions.
diff --git a/crypto/err/openssl.txt b/crypto/err/openssl.txt
@@ -1,4 +1,4 @@
-# Copyright 1999-2020 The OpenSSL Project Authors. All Rights Reserved.
+# Copyright 1999-2021 The OpenSSL Project Authors. All Rights Reserved.
 #
 # Licensed under the OpenSSL license (the "License").  You may not use
 # this file except in compliance with the License.  You can obtain a copy
@@ -2283,6 +2283,7 @@ EVP_R_ONLY_ONESHOT_SUPPORTED:177:only oneshot supported
 EVP_R_OPERATION_NOT_SUPPORTED_FOR_THIS_KEYTYPE:150:\
 	operation not supported for this keytype
 EVP_R_OPERATON_NOT_INITIALIZED:151:operaton not initialized
+EVP_R_OUTPUT_WOULD_OVERFLOW:184:output would overflow
 EVP_R_PARTIALLY_OVERLAPPING:162:partially overlapping buffers
 EVP_R_PBKDF2_ERROR:181:pbkdf2 error
 EVP_R_PKEY_APPLICATION_ASN1_METHOD_ALREADY_REGISTERED:179:\

diff --git a/crypto/evp/evp_enc.c b/crypto/evp/evp_enc.c
@@ -8,6 +8,7 @@
  */
 
 #include <stdio.h>
+#include <limits.h>
 #include <assert.h>
 #include "internal/cryptlib.h"
 #include <openssl/evp.h>
@@ -355,6 +356,19 @@ static int evp_EncryptDecryptUpdate(EVP_CIPHER_CTX *ctx,
             return 1;
         } else {
             j = bl - i;
+
+            /*
+             * Once we've processed the first j bytes from in, the amount of
+             * data left that is a multiple of the block length is:
+             * (inl - j) & ~(bl - 1)
+             * We must ensure that this amount of data, plus the one block that
+             * we process from ctx->buf does not exceed INT_MAX
+             */
+            if (((inl - j) & ~(bl - 1)) > INT_MAX - bl) {
+                EVPerr(EVP_F_EVP_ENCRYPTDECRYPTUPDATE,
+                       EVP_R_OUTPUT_WOULD_OVERFLOW);
+                return 0;
+            }
             memcpy(&(ctx->buf[i]), in, j);
             inl -= j;
             in += j;
@@ -502,6 +516,19 @@ int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
             EVPerr(EVP_F_EVP_DECRYPTUPDATE, EVP_R_PARTIALLY_OVERLAPPING);
             return 0;
         }
+        /*
+         * final_used is only ever set if buf_len is 0. Therefore the maximum
+         * length output we will ever see from evp_EncryptDecryptUpdate is
+         * the maximum multiple of the block length that is <= inl, or just:
+         * inl & ~(b - 1)
+         * Since final_used has been set then the final output length is:
+         * (inl & ~(b - 1)) + b
+         * This must never exceed INT_MAX
+         */
+        if ((inl & ~(b - 1)) > INT_MAX - b) {
+            EVPerr(EVP_F_EVP_DECRYPTUPDATE, EVP_R_OUTPUT_WOULD_OVERFLOW);
+            return 0;
+        }
         memcpy(out, ctx->final, b);
         out += b;
         fix_len = 1;

diff --git a/crypto/evp/evp_err.c b/crypto/evp/evp_err.c
@@ -1,6 +1,6 @@
 /*
  * Generated by util/mkerr.pl DO NOT EDIT
- * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -239,6 +239,8 @@ static const ERR_STRING_DATA EVP_str_reasons[] = {
     "operation not supported for this keytype"},
     {ERR_PACK(ERR_LIB_EVP, 0, EVP_R_OPERATON_NOT_INITIALIZED),
     "operaton not initialized"},
+    {ERR_PACK(ERR_LIB_EVP, 0, EVP_R_OUTPUT_WOULD_OVERFLOW),
+    "output would overflow"},
     {ERR_PACK(ERR_LIB_EVP, 0, EVP_R_PARTIALLY_OVERLAPPING),
     "partially overlapping buffers"},
     {ERR_PACK(ERR_LIB_EVP, 0, EVP_R_PBKDF2_ERROR), "pbkdf2 error"},

diff --git a/include/openssl/evperr.h b/include/openssl/evperr.h
@@ -1,6 +1,6 @@
 /*
  * Generated by util/mkerr.pl DO NOT EDIT
- * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -11,9 +11,7 @@
 #ifndef HEADER_EVPERR_H
 # define HEADER_EVPERR_H
 
-# ifndef HEADER_SYMHACKS_H
-#  include <openssl/symhacks.h>
-# endif
+# include <openssl/symhacks.h>
 
 # ifdef  __cplusplus
 extern "C"
@@ -179,6 +177,7 @@ int ERR_load_EVP_strings(void);
 # define EVP_R_ONLY_ONESHOT_SUPPORTED                     177
 # define EVP_R_OPERATION_NOT_SUPPORTED_FOR_THIS_KEYTYPE   150
 # define EVP_R_OPERATON_NOT_INITIALIZED                   151
+# define EVP_R_OUTPUT_WOULD_OVERFLOW                      184
 # define EVP_R_PARTIALLY_OVERLAPPING                      162
 # define EVP_R_PBKDF2_ERROR                               181
 # define EVP_R_PKEY_APPLICATION_ASN1_METHOD_ALREADY_REGISTERED 179