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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
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@@ -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;