ovl: don't use a temp buf for encoding real fh

We can allocate maximum fh size and encode into it directly.

Suggested-by: Al Viro <[e-mail]>
Signed-off-by: Amir Goldstein <[e-mail]>
Signed-off-by: Miklos Szeredi <[e-mail]>

fs/overlayfs/copy_up.c

···
 struct ovl_fh *ovl_encode_real_fh(struct dentry *real, bool is_upper)
 {
 	struct ovl_fh *fh;
-	int fh_type, fh_len, dwords;
-	void *buf;
+	int fh_type, dwords;
 	int buflen = MAX_HANDLE_SZ;
 	uuid_t *uuid = &real->d_sb->s_uuid;
+	int err;
 
-	buf = kmalloc(buflen, GFP_KERNEL);
-	if (!buf)
+	/* Make sure the real fid stays 32bit aligned */
+	BUILD_BUG_ON(OVL_FH_FID_OFFSET % 4);
+	BUILD_BUG_ON(MAX_HANDLE_SZ + OVL_FH_FID_OFFSET > 255);
+
+	fh = kzalloc(buflen + OVL_FH_FID_OFFSET, GFP_KERNEL);
+	if (!fh)
 		return ERR_PTR(-ENOMEM);
 
 	/*
···
 	 * the price or reconnecting the dentry.
 	 */
 	dwords = buflen >> 2;
-	fh_type = exportfs_encode_fh(real, buf, &dwords, 0);
+	fh_type = exportfs_encode_fh(real, (void *)fh->fb.fid, &dwords, 0);
 	buflen = (dwords << 2);
 
-	fh = ERR_PTR(-EIO);
+	err = -EIO;
 	if (WARN_ON(fh_type < 0) ||
 	    WARN_ON(buflen > MAX_HANDLE_SZ) ||
 	    WARN_ON(fh_type == FILEID_INVALID))
-		goto out;
-
-	/* Make sure the real fid stays 32bit aligned */
-	BUILD_BUG_ON(OVL_FH_FID_OFFSET % 4);
-	BUILD_BUG_ON(MAX_HANDLE_SZ + OVL_FH_FID_OFFSET > 255);
-	fh_len = OVL_FH_FID_OFFSET + buflen;
-	fh = kzalloc(fh_len, GFP_KERNEL);
-	if (!fh) {
-		fh = ERR_PTR(-ENOMEM);
-		goto out;
-	}
+		goto out_err;
 
 	fh->fb.version = OVL_FH_VERSION;
 	fh->fb.magic = OVL_FH_MAGIC;
···
 	 */
 	if (is_upper)
 		fh->fb.flags |= OVL_FH_FLAG_PATH_UPPER;
-	fh->fb.len = fh_len - OVL_FH_WIRE_OFFSET;
+	fh->fb.len = sizeof(fh->fb) + buflen;
 	fh->fb.uuid = *uuid;
-	memcpy(fh->fb.fid, buf, buflen);
 
-out:
-	kfree(buf);
 	return fh;
+
+out_err:
+	kfree(fh);
+	return ERR_PTR(err);
 }
 
 int ovl_set_origin(struct dentry *dentry, struct dentry *lower,