vfs: introduce d_instantiate_no_diralias()
...which just returns -EBUSY if a directory alias would be created.
This is to be used by fuse mkdir to make sure that a buggy or malicious
userspace filesystem doesn't do anything nasty. Previously fuse used a
private mutex for this purpose, which can now go away.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/dcache.c b/fs/dcache.c
index d888223..c8e83d0 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1801,6 +1801,33 @@
EXPORT_SYMBOL(d_instantiate_unique);
+/**
+ * d_instantiate_no_diralias - instantiate a non-aliased dentry
+ * @entry: dentry to complete
+ * @inode: inode to attach to this dentry
+ *
+ * Fill in inode information in the entry. If a directory alias is found, then
+ * return an error (and drop inode). Together with d_materialise_unique() this
+ * guarantees that a directory inode may never have more than one alias.
+ */
+int d_instantiate_no_diralias(struct dentry *entry, struct inode *inode)
+{
+ BUG_ON(!hlist_unhashed(&entry->d_alias));
+
+ spin_lock(&inode->i_lock);
+ if (S_ISDIR(inode->i_mode) && !hlist_empty(&inode->i_dentry)) {
+ spin_unlock(&inode->i_lock);
+ iput(inode);
+ return -EBUSY;
+ }
+ __d_instantiate(entry, inode);
+ spin_unlock(&inode->i_lock);
+ security_d_instantiate(entry, inode);
+
+ return 0;
+}
+EXPORT_SYMBOL(d_instantiate_no_diralias);
+
struct dentry *d_make_root(struct inode *root_inode)
{
struct dentry *res = NULL;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index b7989f2..c3eb2c4 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -342,24 +342,6 @@
return err;
}
-static struct dentry *fuse_materialise_dentry(struct dentry *dentry,
- struct inode *inode)
-{
- struct dentry *newent;
-
- if (inode && S_ISDIR(inode->i_mode)) {
- struct fuse_conn *fc = get_fuse_conn(inode);
-
- mutex_lock(&fc->inst_mutex);
- newent = d_materialise_unique(dentry, inode);
- mutex_unlock(&fc->inst_mutex);
- } else {
- newent = d_materialise_unique(dentry, inode);
- }
-
- return newent;
-}
-
static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
unsigned int flags)
{
@@ -382,7 +364,7 @@
if (inode && get_node_id(inode) == FUSE_ROOT_ID)
goto out_iput;
- newent = fuse_materialise_dentry(entry, inode);
+ newent = d_materialise_unique(entry, inode);
err = PTR_ERR(newent);
if (IS_ERR(newent))
goto out_err;
@@ -601,21 +583,9 @@
}
kfree(forget);
- if (S_ISDIR(inode->i_mode)) {
- struct dentry *alias;
- mutex_lock(&fc->inst_mutex);
- alias = d_find_alias(inode);
- if (alias) {
- /* New directory must have moved since mkdir */
- mutex_unlock(&fc->inst_mutex);
- dput(alias);
- iput(inode);
- return -EBUSY;
- }
- d_instantiate(entry, inode);
- mutex_unlock(&fc->inst_mutex);
- } else
- d_instantiate(entry, inode);
+ err = d_instantiate_no_diralias(entry, inode);
+ if (err)
+ return err;
fuse_change_entry_timeout(entry, &outarg);
fuse_invalidate_attr(dir);
@@ -1284,7 +1254,7 @@
if (!inode)
goto out;
- alias = fuse_materialise_dentry(dentry, inode);
+ alias = d_materialise_unique(dentry, inode);
err = PTR_ERR(alias);
if (IS_ERR(alias))
goto out;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 5b9e6f3..fe446c2 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -374,9 +374,6 @@
/** Lock protecting accessess to members of this structure */
spinlock_t lock;
- /** Mutex protecting against directory alias creation */
- struct mutex inst_mutex;
-
/** Refcount */
atomic_t count;
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index a8ce6da..1c15613 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -565,7 +565,6 @@
{
memset(fc, 0, sizeof(*fc));
spin_lock_init(&fc->lock);
- mutex_init(&fc->inst_mutex);
init_rwsem(&fc->killsb);
atomic_set(&fc->count, 1);
init_waitqueue_head(&fc->waitq);
@@ -596,7 +595,6 @@
if (atomic_dec_and_test(&fc->count)) {
if (fc->destroy_req)
fuse_request_free(fc->destroy_req);
- mutex_destroy(&fc->inst_mutex);
fc->release(fc);
}
}
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 59066e0..716c376 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -224,6 +224,7 @@
extern void d_instantiate(struct dentry *, struct inode *);
extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
extern struct dentry * d_materialise_unique(struct dentry *, struct inode *);
+extern int d_instantiate_no_diralias(struct dentry *, struct inode *);
extern void __d_drop(struct dentry *dentry);
extern void d_drop(struct dentry *dentry);
extern void d_delete(struct dentry *);