fuse_dentry_revalidate(): use stable parent inode and name passed by caller

No need to mess with dget_parent() for the former; for the latter we really should
not rely upon ->d_name.name remaining stable - it's a real-life UAF.

Reviewed-by: Jeff Layton <[email protected]>
Acked-by: Miklos Szeredi <[email protected]>
Signed-off-by: Al Viro <[email protected]>

Author: Al Viro

fs/fuse/dir.c

@@ -175,9 +175,11 @@ static void fuse_lookup_init(struct fuse_conn *fc, struct fuse_args *args,
 	memset(outarg, 0, sizeof(struct fuse_entry_out));
 	args->opcode = FUSE_LOOKUP;
 	args->nodeid = nodeid;
-	args->in_numargs = 1;
-	args->in_args[0].size = name->len + 1;
+	args->in_numargs = 2;
+	args->in_args[0].size = name->len;
 	args->in_args[0].value = name->name;
+	args->in_args[1].size = 1;
+	args->in_args[1].value = "";
 	args->out_numargs = 1;
 	args->out_args[0].size = sizeof(struct fuse_entry_out);
 	args->out_args[0].value = outarg;
@@ -196,7 +198,6 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
 				  struct dentry *entry, unsigned int flags)
 {
 	struct inode *inode;
-	struct dentry *parent;
 	struct fuse_mount *fm;
 	struct fuse_inode *fi;
 	int ret;
@@ -228,11 +229,9 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
 
 		attr_version = fuse_get_attr_version(fm->fc);
 
-		parent = dget_parent(entry);
-		fuse_lookup_init(fm->fc, &args, get_node_id(d_inode(parent)),
-				 &entry->d_name, &outarg);
+		fuse_lookup_init(fm->fc, &args, get_node_id(dir),
+				 name, &outarg);
 		ret = fuse_simple_request(fm, &args);
-		dput(parent);
 		/* Zero nodeid is same as -ENOENT */
 		if (!ret && !outarg.nodeid)
 			ret = -ENOENT;
@@ -266,9 +265,7 @@ static int fuse_dentry_revalidate(struct inode *dir, const struct qstr *name,
 			if (test_bit(FUSE_I_INIT_RDPLUS, &fi->state))
 				return -ECHILD;
 		} else if (test_and_clear_bit(FUSE_I_INIT_RDPLUS, &fi->state)) {
-			parent = dget_parent(entry);
-			fuse_advise_use_readdirplus(d_inode(parent));
-			dput(parent);
+			fuse_advise_use_readdirplus(dir);
 		}
 	}
 	ret = 1;