fuse: fix illegal access to inode with reused nodeid

Server responds to LOOKUP and other ops (READDIRPLUS/CREATE/MKNOD/...)
with ourarg containing nodeid and generation.

If a fuse inode is found in inode cache with the same nodeid but different
generation, the existing fuse inode should be unhashed and marked "bad" and
a new inode with the new generation should be hashed instead.

This can happen, for example, with passhrough fuse filesystem that returns
the real filesystem ino/generation on lookup and where real inode numbers
can get recycled due to real files being unlinked not via the fuse
passthrough filesystem.

With current code, this situation will not be detected and an old fuse
dentry that used to point to an older generation real inode, can be used to
access a completely new inode, which should be accessed only via the new
dentry.

Note that because the FORGET message carries the nodeid w/o generation, the
server should wait to get FORGET counts for the nlookup counts of the old
and reused inodes combined, before it can free the resources associated to
that nodeid.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dir.c

@@ -252,7 +252,7 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 		if (ret == -ENOMEM)
 			goto out;
 		if (ret || fuse_invalid_attr(&outarg.attr) ||
-		    inode_wrong_type(inode, outarg.attr.mode))
+		    fuse_stale_inode(inode, outarg.generation, &outarg.attr))
 			goto invalid;
 
 		forget_all_cached_acls(inode);

fs/fuse/fuse_i.h

@@ -870,6 +870,13 @@ static inline u64 fuse_get_attr_version(struct fuse_conn *fc)
 	return atomic64_read(&fc->attr_version);
 }
 
+static inline bool fuse_stale_inode(const struct inode *inode, int generation,
+				    struct fuse_attr *attr)
+{
+	return inode->i_generation != generation ||
+		inode_wrong_type(inode, attr->mode);
+}
+
 static inline void fuse_make_bad(struct inode *inode)
 {
 	remove_inode_hash(inode);

fs/fuse/inode.c

@@ -350,8 +350,8 @@ struct inode *fuse_iget(struct super_block *sb, u64 nodeid,
 		inode->i_generation = generation;
 		fuse_init_inode(inode, attr);
 		unlock_new_inode(inode);
-	} else if (inode_wrong_type(inode, attr->mode)) {
-		/* Inode has changed type, any I/O on the old should fail */
+	} else if (fuse_stale_inode(inode, generation, attr)) {
+		/* nodeid was reused, any I/O on the old inode should fail */
 		fuse_make_bad(inode);
 		iput(inode);
 		goto retry;

fs/fuse/readdir.c

@@ -200,9 +200,12 @@ static int fuse_direntplus_link(struct file *file,
 	if (!d_in_lookup(dentry)) {
 		struct fuse_inode *fi;
 		inode = d_inode(dentry);
+		if (inode && get_node_id(inode) != o->nodeid)
+			inode = NULL;
 		if (!inode ||
-		    get_node_id(inode) != o->nodeid ||
-		    inode_wrong_type(inode, o->attr.mode)) {
+		    fuse_stale_inode(inode, o->generation, &o->attr)) {
+			if (inode)
+				fuse_make_bad(inode);
 			d_invalidate(dentry);
 			dput(dentry);
 			goto retry;