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: Zefan Li <lizefan@huawei.com>

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index ea9931281557ad8d3ed4049b48c66110df5f0811..3d0633891f286e86c0f601d627be10292d587c0d 100644 (file)
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -2044,7 +2044,6 @@ 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;
                }