fuse: fix readdirplus Oops in fuse_dentry_revalidate

Fix bug introduced by commit 4582a4ab "FUSE: Adapt readdirplus to application
usage patterns".

We need to check for a positive dentry; negative dentries are not added by
readdirplus.  Secondly we need to advise the use of readdirplus on the *parent*,
otherwise the whole thing is useless.  Thirdly all this is only relevant if
"readdirplus_auto" mode is selected by the filesystem.

We advise the use of readdirplus only if the dentry was still valid.  If we had
to redo the lookup then there was no use in doing the -plus version.
Reported-by: Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: Feng Shuo <steve.shuo.feng@gmail.com>
CC: stable@vger.kernel.org

fs/fuse/dir.c

@@ -180,6 +180,8 @@ u64 fuse_get_attr_version(struct fuse_conn *fc)
 static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 {
 	struct inode *inode;
+	struct dentry *parent;
+	struct fuse_conn *fc;
 
 	inode = ACCESS_ONCE(entry->d_inode);
 	if (inode && is_bad_inode(inode))
@@ -187,10 +189,8 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 	else if (fuse_dentry_time(entry) < get_jiffies_64()) {
 		int err;
 		struct fuse_entry_out outarg;
-		struct fuse_conn *fc;
 		struct fuse_req *req;
 		struct fuse_forget_link *forget;
-		struct dentry *parent;
 		u64 attr_version;
 
 		/* For negative dentries, always do a fresh lookup */
@@ -241,8 +241,14 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 				       entry_attr_timeout(&outarg),
 				       attr_version);
 		fuse_change_entry_timeout(entry, &outarg);
+	} else if (inode) {
+		fc = get_fuse_conn(inode);
+		if (fc->readdirplus_auto) {
+			parent = dget_parent(entry);
+			fuse_advise_use_readdirplus(parent->d_inode);
+			dput(parent);
+		}
 	}
-	fuse_advise_use_readdirplus(inode);
 	return 1;
 }
 

fs/fuse/inode.c

@@ -867,10 +867,11 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 				fc->dont_mask = 1;
 			if (arg->flags & FUSE_AUTO_INVAL_DATA)
 				fc->auto_inval_data = 1;
-			if (arg->flags & FUSE_DO_READDIRPLUS)
+			if (arg->flags & FUSE_DO_READDIRPLUS) {
 				fc->do_readdirplus = 1;
 				if (arg->flags & FUSE_READDIRPLUS_AUTO)
 					fc->readdirplus_auto = 1;
+			}
 			if (arg->flags & FUSE_ASYNC_DIO)
 				fc->async_dio = 1;
 		} else {