bpo-33770: improve base64 exception message for encoded inputs of invalid length (GH-7416) (GH-7602)
(cherry picked from commit 1b85c71a2136d3fa6a1da05b27b1fe4e4b8ee45e)
Co-authored-by: Tal Einat <taleinat+github@gmail.com>
diff --git a/Lib/test/test_binascii.py b/Lib/test/test_binascii.py
index 8fa57cd..7418a9ce9 100644
--- a/Lib/test/test_binascii.py
+++ b/Lib/test/test_binascii.py
@@ -110,6 +110,34 @@
# empty strings. TBD: shouldn't it raise an exception instead ?
self.assertEqual(binascii.a2b_base64(self.type2test(fillers)), b'')
+ def test_base64errors(self):
+ # Test base64 with invalid padding
+ def assertIncorrectPadding(data):
+ with self.assertRaisesRegex(binascii.Error, r'(?i)Incorrect padding'):
+ binascii.a2b_base64(self.type2test(data))
+
+ assertIncorrectPadding(b'ab')
+ assertIncorrectPadding(b'ab=')
+ assertIncorrectPadding(b'abc')
+ assertIncorrectPadding(b'abcdef')
+ assertIncorrectPadding(b'abcdef=')
+ assertIncorrectPadding(b'abcdefg')
+ assertIncorrectPadding(b'a=b=')
+ assertIncorrectPadding(b'a\nb=')
+
+ # Test base64 with invalid number of valid characters (1 mod 4)
+ def assertInvalidLength(data):
+ with self.assertRaisesRegex(binascii.Error, r'(?i)invalid.+length'):
+ binascii.a2b_base64(self.type2test(data))
+
+ assertInvalidLength(b'a')
+ assertInvalidLength(b'a=')
+ assertInvalidLength(b'a==')
+ assertInvalidLength(b'a===')
+ assertInvalidLength(b'a' * 5)
+ assertInvalidLength(b'a' * (4 * 87 + 1))
+ assertInvalidLength(b'A\tB\nC ??DE') # only 5 valid characters
+
def test_uu(self):
MAX_UU = 45
for backtick in (True, False):
diff --git a/Misc/NEWS.d/next/Library/2018-06-05-11-29-26.bpo-33770.oBhxxw.rst b/Misc/NEWS.d/next/Library/2018-06-05-11-29-26.bpo-33770.oBhxxw.rst
new file mode 100644
index 0000000..a1529dd
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2018-06-05-11-29-26.bpo-33770.oBhxxw.rst
@@ -0,0 +1 @@
+improve base64 exception message for encoded inputs of invalid length
diff --git a/Modules/binascii.c b/Modules/binascii.c
index 1af6b7f..2df80af 100644
--- a/Modules/binascii.c
+++ b/Modules/binascii.c
@@ -510,7 +510,18 @@
}
if (leftbits != 0) {
- PyErr_SetString(Error, "Incorrect padding");
+ if (leftbits == 6) {
+ /*
+ ** There is exactly one extra valid, non-padding, base64 character.
+ ** This is an invalid length, as there is no possible input that
+ ** could encoded into such a base64 string.
+ */
+ PyErr_SetString(Error,
+ "Invalid base64-encoded string: "
+ "length cannot be 1 more than a multiple of 4");
+ } else {
+ PyErr_SetString(Error, "Incorrect padding");
+ }
_PyBytesWriter_Dealloc(&writer);
return NULL;
}