Issue #28275: Merge bz2 fix from 3.5 into 3.6

Lib/test/test_bz2.py

@@ -821,6 +821,12 @@ class BZ2DecompressorTest(BaseTest):
         out.append(bzd.decompress(self.DATA[300:]))
         self.assertEqual(b''.join(out), self.TEXT)
 
+    def test_failure(self):
+        bzd = BZ2Decompressor()
+        self.assertRaises(Exception, bzd.decompress, self.BAD_DATA * 30)
+        # Previously, a second call could crash due to internal inconsistency
+        self.assertRaises(Exception, bzd.decompress, self.BAD_DATA * 30)
+
 class CompressDecompressTest(BaseTest):
     def testCompress(self):
         data = bz2.compress(self.TEXT)

Lib/test/test_lzma.py

@@ -249,11 +249,9 @@ class CompressorDecompressorTestCase(unittest.TestCase):
     def test_decompressor_bug_28275(self):
         # Test coverage for Issue 28275
         lzd = LZMADecompressor()
-        for i in range(2):
-            try:
-                lzd.decompress(COMPRESSED_RAW_1)
-            except LZMAError:
-                pass
+        self.assertRaises(LZMAError, lzd.decompress, COMPRESSED_RAW_1)
+        # Previously, a second call could crash due to internal inconsistency
+        self.assertRaises(LZMAError, lzd.decompress, COMPRESSED_RAW_1)
 
     # Test that LZMACompressor->LZMADecompressor preserves the input data.
 

Misc/NEWS

@@ -67,7 +67,8 @@ Library
   that they don't call itermonthdates() which can cause datetime.date
   under/overflow.
 
-- Issue #28275: Fixed possible use adter free in LZMADecompressor.decompress().
+- Issue #28275: Fixed possible use after free in the decompress()
+  methods of the LZMADecompressor and BZ2Decompressor classes.
   Original patch by John Leitch.
 
 - Issue #27897: Fixed possible crash in sqlite3.Connection.create_collation()

Modules/_bz2module.c

@@ -534,8 +534,10 @@ decompress(BZ2Decompressor *d, char *data, size_t len, Py_ssize_t max_length)
     }
 
     result = decompress_buf(d, max_length);
-    if(result == NULL)
+    if(result == NULL) {
+        bzs->next_in = NULL;
         return NULL;
+    }
 
     if (d->eof) {
         d->needs_input = 0;