ext4: only use fscrypt_zeroout_range() on regular files

fscrypt_zeroout_range() is only for encrypted regular files, not for
encrypted directories or symlinks.

Fortunately, currently it seems it's never called on non-regular files.
But to be safe ext4 should explicitly check S_ISREG() before calling it.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20191226161022.53490-1-ebiggers@kernel.orgSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -403,7 +403,7 @@ int ext4_issue_zeroout(struct inode *inode, ext4_lblk_t lblk, ext4_fsblk_t pblk,
 {
 	int ret;
 
-	if (IS_ENCRYPTED(inode))
+	if (IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode))
 		return fscrypt_zeroout_range(inode, lblk, pblk, len);
 
 	ret = sb_issue_zeroout(inode->i_sb, pblk, len, GFP_NOFS);