eCryptfs: Remove unnecessary grow_file() function

When creating a new eCryptfs file, the crypto metadata is written out
and then the lower file was being "grown" with 4 kB of encrypted zeroes.
I suspect that growing the encrypted file was to prevent an information
leak that the unencrypted file was empty. However, the unencrypted file
size is stored, in plaintext, in the metadata so growing the file is
unnecessary.

Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index bfd8b68..98a2a31 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1389,6 +1389,7 @@
 		rc = -ENOMEM;
 		goto out;
 	}
+	/* Zeroed page ensures the in-header unencrypted i_size is set to 0 */
 	rc = ecryptfs_write_headers_virt(virt, virt_len, &size, crypt_stat,
 					 ecryptfs_dentry);
 	if (unlikely(rc)) {