eCryptfs: Remove buggy and unnecessary write in file name decode routine

commit 942080643bce061c3dd9d5718d3b745dcb39a8bc upstream.

Dmitry Chernenkov used KASAN to discover that eCryptfs writes past the
end of the allocated buffer during encrypted filename decoding. This
fix corrects the issue by getting rid of the unnecessary 0 write when
the current bit offset is 2.

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Reported-by: Dmitry Chernenkov <dmitryc@google.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 000eae2782b6e905aefa05980ef91c54b81a8274..bf926f7a5f0c3893eb9b725d3257e1269f0a9aad 100644 (file)
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1917,7 +1917,6 @@ ecryptfs_decode_from_filename(unsigned char *dst, size_t *dst_size,
                        break;
                case 2:
                        dst[dst_byte_offset++] |= (src_byte);
-                       dst[dst_byte_offset] = 0;
                        current_bit_offset = 0;
                        break;
                }