f2fs: fix leaking uninitialized memory in compressed clusters

When the compressed data of a cluster doesn't end on a page boundary,
the remainder of the last page must be zeroed in order to avoid leaking
uninitialized memory to disk.

Fixes: 4c8ff709 ("f2fs: support data compression")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -385,11 +385,15 @@ static int f2fs_compress_pages(struct compress_ctx *cc)
 	for (i = 0; i < COMPRESS_DATA_RESERVED_SIZE; i++)
 		cc->cbuf->reserved[i] = cpu_to_le32(0);
 
+	nr_cpages = DIV_ROUND_UP(cc->clen + COMPRESS_HEADER_SIZE, PAGE_SIZE);
+
+	/* zero out any unused part of the last page */
+	memset(&cc->cbuf->cdata[cc->clen], 0,
+	       (nr_cpages * PAGE_SIZE) - (cc->clen + COMPRESS_HEADER_SIZE));
+
 	vunmap(cc->cbuf);
 	vunmap(cc->rbuf);
 
-	nr_cpages = DIV_ROUND_UP(cc->clen + COMPRESS_HEADER_SIZE, PAGE_SIZE);
-
 	for (i = nr_cpages; i < cc->nr_cpages; i++) {
 		f2fs_put_compressed_page(cc->cpages[i]);
 		cc->cpages[i] = NULL;