python: implement getBlockMode for CryptographicOperations

python/ql/lib/semmle/python/Concepts.qll

@@ -1226,6 +1226,13 @@ module Cryptography {
 
     /** Gets an input the algorithm is used on, for example the plain text input to be encrypted. */
     DataFlow::Node getAnInput() { result = super.getAnInput() }
+
+    /**
+     * Gets the block mode used to perform this cryptographic operation.
+     * This may have no result - for example if the `CryptographicAlgorithm` used
+     * is a stream cipher rather than a block cipher.
+     */
+    BlockMode getBlockMode() { result = super.getBlockMode() }
   }
 
   /** Provides classes for modeling new applications of a cryptographic algorithms. */
@@ -1243,6 +1250,24 @@ module Cryptography {
 
       /** Gets an input the algorithm is used on, for example the plain text input to be encrypted. */
       abstract DataFlow::Node getAnInput();
+
+      /**
+       * Gets the block mode used to perform this cryptographic operation.
+       * This may have no result - for example if the `CryptographicAlgorithm` used
+       * is a stream cipher rather than a block cipher.
+       */
+      abstract BlockMode getBlockMode();
     }
   }
+
+  /**
+   * A cryptographic block cipher mode of operation. This can be used to encrypt
+   * data of arbitrary length using a block encryption algorithm.
+   */
+  class BlockMode extends string {
+    BlockMode() { this = ["ECB", "CBC", "GCM", "CCM", "CFB", "OFB", "CTR", "OPENPGP"] }
+
+    /** Holds if this block mode is considered to be insecure. */
+    predicate isWeak() { this = "ECB" }
+  }
 }

python/ql/lib/semmle/python/frameworks/Cryptodome.qll

@@ -108,20 +108,20 @@ private module CryptodomeModel {
     DataFlow::CallCfgNode {
     string methodName;
     string cipherName;
+    API::CallNode newCall;
 
     CryptodomeGenericCipherOperation() {
       methodName in [
           "encrypt", "decrypt", "verify", "update", "hexverify", "encrypt_and_digest",
           "decrypt_and_verify"
         ] and
-      this =
+      newCall =
         API::moduleImport(["Crypto", "Cryptodome"])
             .getMember("Cipher")
             .getMember(cipherName)
             .getMember("new")
-            .getReturn()
-            .getMember(methodName)
-            .getACall()
+            .getACall() and
+      this = newCall.getReturn().getMember(methodName).getACall()
     }
 
     override Cryptography::CryptographicAlgorithm getAlgorithm() { result.matchesName(cipherName) }
@@ -155,6 +155,20 @@ private module CryptodomeModel {
           this.getArgByName("mac_tag")
         ]
     }
+
+    override Cryptography::BlockMode getBlockMode() {
+      // `modeName` is of the form "MODE_<BlockMode>"
+      exists(string modeName |
+        newCall.getArg(1) =
+          API::moduleImport(["Crypto", "Cryptodome"])
+              .getMember("Cipher")
+              .getMember(cipherName)
+              .getMember(modeName)
+              .getAUse()
+      |
+        result = modeName.splitAt("_", 1)
+      )
+    }
   }
 
   /**
@@ -192,6 +206,8 @@ private module CryptodomeModel {
         result in [this.getArg(1), this.getArgByName("signature")]
       )
     }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -215,5 +231,7 @@ private module CryptodomeModel {
     override Cryptography::CryptographicAlgorithm getAlgorithm() { result.matchesName(hashName) }
 
     override DataFlow::Node getAnInput() { result in [this.getArg(0), this.getArgByName("data")] }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 }

python/ql/lib/semmle/python/frameworks/Cryptography.qll

@@ -170,8 +170,19 @@ private module CryptographyModel {
             .getMember(algorithmName)
     }
 
+    /** Gets a reference to a `cryptography.hazmat.primitives.ciphers.modes` Class */
+    API::Node modeClassRef(string modeName) {
+      result =
+        API::moduleImport("cryptography")
+            .getMember("hazmat")
+            .getMember("primitives")
+            .getMember("ciphers")
+            .getMember("modes")
+            .getMember(modeName)
+    }
+
     /** Gets a reference to a Cipher instance using algorithm with `algorithmName`. */
-    API::Node cipherInstance(string algorithmName) {
+    API::Node cipherInstance(string algorithmName, string modeName) {
       exists(API::CallNode call | result = call.getReturn() |
         call =
           API::moduleImport("cryptography")
@@ -182,7 +193,12 @@ private module CryptographyModel {
               .getACall() and
         algorithmClassRef(algorithmName).getReturn().getAUse() in [
             call.getArg(0), call.getArgByName("algorithm")
-          ]
+          ] and
+        exists(DataFlow::Node modeArg | modeArg in [call.getArg(1), call.getArgByName("mode")] |
+          modeArg = modeClassRef(modeName).getReturn().getAUse()
+          or
+          modeArg.asExpr() instanceof None and modeName = "<none>"
+        )
       )
     }
 
@@ -192,10 +208,11 @@ private module CryptographyModel {
     class CryptographyGenericCipherOperation extends Cryptography::CryptographicOperation::Range,
       DataFlow::MethodCallNode {
       string algorithmName;
+      string modeName;
 
       CryptographyGenericCipherOperation() {
         this =
-          cipherInstance(algorithmName)
+          cipherInstance(algorithmName, modeName)
               .getMember(["decryptor", "encryptor"])
               .getReturn()
               .getMember(["update", "update_into"])
@@ -207,6 +224,8 @@ private module CryptographyModel {
       }
 
       override DataFlow::Node getAnInput() { result in [this.getArg(0), this.getArgByName("data")] }
+
+      override Cryptography::BlockMode getBlockMode() { result = modeName }
     }
   }
 
@@ -257,6 +276,8 @@ private module CryptographyModel {
       }
 
       override DataFlow::Node getAnInput() { result in [this.getArg(0), this.getArgByName("data")] }
+
+      override Cryptography::BlockMode getBlockMode() { none() }
     }
   }
 }

python/ql/lib/semmle/python/frameworks/Rsa.qll

@@ -41,6 +41,8 @@ private module Rsa {
     override DataFlow::Node getAnInput() {
       result in [this.getArg(0), this.getArgByName("message")]
     }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -54,6 +56,8 @@ private module Rsa {
     override Cryptography::CryptographicAlgorithm getAlgorithm() { result.getName() = "RSA" }
 
     override DataFlow::Node getAnInput() { result in [this.getArg(0), this.getArgByName("crypto")] }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -79,6 +83,8 @@ private module Rsa {
     override DataFlow::Node getAnInput() {
       result in [this.getArg(0), this.getArgByName("message")]
     }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -100,6 +106,8 @@ private module Rsa {
       or
       result in [this.getArg(1), this.getArgByName("signature")]
     }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -122,6 +130,8 @@ private module Rsa {
     override DataFlow::Node getAnInput() {
       result in [this.getArg(0), this.getArgByName("message")]
     }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -137,5 +147,7 @@ private module Rsa {
     override DataFlow::Node getAnInput() {
       result in [this.getArg(0), this.getArgByName("hash_value")]
     }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 }

python/ql/lib/semmle/python/frameworks/Stdlib.qll

@@ -2671,6 +2671,8 @@ private module StdlibPrivate {
     override Cryptography::CryptographicAlgorithm getAlgorithm() { result.matchesName(hashName) }
 
     override DataFlow::Node getAnInput() { result = this.getParameter(1, "data").getARhs() }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**
@@ -2686,6 +2688,8 @@ private module StdlibPrivate {
     override Cryptography::CryptographicAlgorithm getAlgorithm() { result.matchesName(hashName) }
 
     override DataFlow::Node getAnInput() { result = this.getArg(0) }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /** Helper predicate for the `HashLibGenericHashOperation` charpred, to prevent a bad join order. */
@@ -2709,6 +2713,8 @@ private module StdlibPrivate {
     HashlibGenericHashOperation() { hashClass = hashlibMember(hashName) }
 
     override Cryptography::CryptographicAlgorithm getAlgorithm() { result.matchesName(hashName) }
+
+    override Cryptography::BlockMode getBlockMode() { none() }
   }
 
   /**