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vfs: introduce d_instantiate_no_diralias()

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...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>
This commit is contained in:
Miklos Szeredi 2013-10-01 16:44:54 +02:00 committed by Al Viro
parent 94e92a6e77
commit b70a80e7a1
5 changed files with 33 additions and 40 deletions
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27
fs/dcache.c
View File

@ -1801,6 +1801,33 @@ struct dentry *d_instantiate_unique(struct dentry *entry, struct inode *inode)
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;

40
fs/fuse/dir.c
View File

@ -342,24 +342,6 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
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 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
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 @@ static int create_new_entry(struct fuse_conn *fc, struct fuse_req *req,
}
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 @@ static int fuse_direntplus_link(struct file *file,
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;

3
fs/fuse/fuse_i.h
View File

@ -374,9 +374,6 @@ struct fuse_conn {
/** 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;

2
fs/fuse/inode.c
View File

@ -565,7 +565,6 @@ void fuse_conn_init(struct fuse_conn *fc)
{
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 @@ void fuse_conn_put(struct fuse_conn *fc)
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);
}
}

1
include/linux/dcache.h
View File

@ -224,6 +224,7 @@ static inline int dname_external(const struct dentry *dentry)
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 *);