alistair23-linux/fs/9p/fid.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * V9FS FID Management
 *
 *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
 *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/idr.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>

#include "v9fs.h"
#include "v9fs_vfs.h"
#include "fid.h"

/**
 * v9fs_fid_add - add a fid to a dentry
 * @dentry: dentry that the fid is being added to
 * @fid: fid to add
 *
 */

static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
{
	hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
}

void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
{
	spin_lock(&dentry->d_lock);
	__add_fid(dentry, fid);
	spin_unlock(&dentry->d_lock);
}

/**
 * v9fs_fid_find - retrieve a fid that belongs to the specified uid
 * @dentry: dentry to look for fid in
 * @uid: return fid that belongs to the specified user
 * @any: if non-zero, return any fid associated with the dentry
 *
 */

static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
{
	struct p9_fid *fid, *ret;

	p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p) uid %d any %d\n",
		 dentry, dentry, from_kuid(&init_user_ns, uid),
		 any);
	ret = NULL;
	/* we'll recheck under lock if there's anything to look in */
	if (dentry->d_fsdata) {
		struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
		spin_lock(&dentry->d_lock);
		hlist_for_each_entry(fid, h, dlist) {
			if (any || uid_eq(fid->uid, uid)) {
				ret = fid;
				break;
			}
		}
		spin_unlock(&dentry->d_lock);
	}

	return ret;
}

/*
 * We need to hold v9ses->rename_sem as long as we hold references
 * to returned path array. Array element contain pointers to
 * dentry names.
 */
static int build_path_from_dentry(struct v9fs_session_info *v9ses,
				  struct dentry *dentry, const unsigned char ***names)
{
	int n = 0, i;
	const unsigned char **wnames;
	struct dentry *ds;

	for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
		n++;

	wnames = kmalloc_array(n, sizeof(char *), GFP_KERNEL);
	if (!wnames)
		goto err_out;

	for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
		wnames[i] = ds->d_name.name;

	*names = wnames;
	return n;
err_out:
	return -ENOMEM;
}

static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
					       kuid_t uid, int any)
{
	struct dentry *ds;
	const unsigned char **wnames, *uname;
	int i, n, l, clone, access;
	struct v9fs_session_info *v9ses;
	struct p9_fid *fid, *old_fid = NULL;

	v9ses = v9fs_dentry2v9ses(dentry);
	access = v9ses->flags & V9FS_ACCESS_MASK;
	fid = v9fs_fid_find(dentry, uid, any);
	if (fid)
		return fid;
	/*
	 * we don't have a matching fid. To do a TWALK we need
	 * parent fid. We need to prevent rename when we want to
	 * look at the parent.
	 */
	down_read(&v9ses->rename_sem);
	ds = dentry->d_parent;
	fid = v9fs_fid_find(ds, uid, any);
	if (fid) {
		/* Found the parent fid do a lookup with that */
		fid = p9_client_walk(fid, 1, &dentry->d_name.name, 1);
		goto fid_out;
	}
	up_read(&v9ses->rename_sem);

	/* start from the root and try to do a lookup */
	fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
	if (!fid) {
		/* the user is not attached to the fs yet */
		if (access == V9FS_ACCESS_SINGLE)
			return ERR_PTR(-EPERM);

		if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
				uname = NULL;
		else
			uname = v9ses->uname;

		fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
				       v9ses->aname);
		if (IS_ERR(fid))
			return fid;

		v9fs_fid_add(dentry->d_sb->s_root, fid);
	}
	/* If we are root ourself just return that */
	if (dentry->d_sb->s_root == dentry)
		return fid;
	/*
	 * Do a multipath walk with attached root.
	 * When walking parent we need to make sure we
	 * don't have a parallel rename happening
	 */
	down_read(&v9ses->rename_sem);
	n  = build_path_from_dentry(v9ses, dentry, &wnames);
	if (n < 0) {
		fid = ERR_PTR(n);
		goto err_out;
	}
	clone = 1;
	i = 0;
	while (i < n) {
		l = min(n - i, P9_MAXWELEM);
		/*
		 * We need to hold rename lock when doing a multipath
		 * walk to ensure none of the patch component change
		 */
		fid = p9_client_walk(fid, l, &wnames[i], clone);
		if (IS_ERR(fid)) {
			if (old_fid) {
				/*
				 * If we fail, clunk fid which are mapping
				 * to path component and not the last component
				 * of the path.
				 */
				p9_client_clunk(old_fid);
			}
			kfree(wnames);
			goto err_out;
		}
		old_fid = fid;
		i += l;
		clone = 0;
	}
	kfree(wnames);
fid_out:
	if (!IS_ERR(fid)) {
		spin_lock(&dentry->d_lock);
		if (d_unhashed(dentry)) {
			spin_unlock(&dentry->d_lock);
			p9_client_clunk(fid);
			fid = ERR_PTR(-ENOENT);
		} else {
			__add_fid(dentry, fid);
			spin_unlock(&dentry->d_lock);
		}
	}
err_out:
	up_read(&v9ses->rename_sem);
	return fid;
}

/**
 * v9fs_fid_lookup - lookup for a fid, try to walk if not found
 * @dentry: dentry to look for fid in
 *
 * Look for a fid in the specified dentry for the current user.
 * If no fid is found, try to create one walking from a fid from the parent
 * dentry (if it has one), or the root dentry. If the user haven't accessed
 * the fs yet, attach now and walk from the root.
 */

struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
{
	kuid_t uid;
	int  any, access;
	struct v9fs_session_info *v9ses;

	v9ses = v9fs_dentry2v9ses(dentry);
	access = v9ses->flags & V9FS_ACCESS_MASK;
	switch (access) {
	case V9FS_ACCESS_SINGLE:
	case V9FS_ACCESS_USER:
	case V9FS_ACCESS_CLIENT:
		uid = current_fsuid();
		any = 0;
		break;

	case V9FS_ACCESS_ANY:
		uid = v9ses->uid;
		any = 1;
		break;

	default:
		uid = INVALID_UID;
		any = 0;
		break;
	}
	return v9fs_fid_lookup_with_uid(dentry, uid, any);
}

struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
{
	int err;
	struct p9_fid *fid;

	fid = clone_fid(v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0));
	if (IS_ERR(fid))
		goto error_out;
	/*
	 * writeback fid will only be used to write back the
	 * dirty pages. We always request for the open fid in read-write
	 * mode so that a partial page write which result in page
	 * read can work.
	 */
	err = p9_client_open(fid, O_RDWR);
	if (err < 0) {
		p9_client_clunk(fid);
		fid = ERR_PTR(err);
		goto error_out;
	}
error_out:
	return fid;
}