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Backport the xattr.c VFS permission checking from 2.6 kernels.
Merge of 2.4.x-xfs-melb:linux:25016a by kenmcd.

/*
  File: fs/xattr.c

  Extended attribute handling.

  Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
  Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
 */
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/smp_lock.h>
#include <linux/file.h>
#include <linux/xattr.h>
#include <asm/uaccess.h>

/*
 * Check permissions for extended attribute access.  This is a bit complicated
 * because different namespaces have very different rules.
 */
static int
xattr_permission(struct inode *inode, const char *name, int mask)
{
	/*
	 * We can never set or remove an extended attribute on a read-only
	 * filesystem  or on an immutable / append-only inode.
	 */
	if (mask & MAY_WRITE) {
		if (IS_RDONLY(inode))
			return -EROFS;
		if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
			return -EPERM;
	}

	/*
	 * No restriction for security.* and system.* from the VFS.  Decision
	 * on these is left to the underlying filesystem / security module.
	 */
	if (!strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) ||
	    !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
		return 0;

	/*
	 * The trusted.* namespace can only accessed by a privilegued user.
	 */
	if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
		return (capable(CAP_SYS_ADMIN) ? 0 : -EPERM);

	if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
		if (!S_ISREG(inode->i_mode) &&
		    (!S_ISDIR(inode->i_mode) || inode->i_mode & S_ISVTX))
			return -EPERM;
	}

	return permission(inode, mask);
}

int
vfs_setxattr(struct dentry *dentry, char *name, void *value,
		size_t size, int flags)
{
	struct inode *inode = dentry->d_inode;
	int error;

	if (!inode->i_op->setxattr)
		return -EOPNOTSUPP;

	error = xattr_permission(inode, name, MAY_WRITE);
	if (error)
		return error;

	down(&inode->i_sem);
	lock_kernel();
	error = inode->i_op->setxattr(dentry, name, value, size, flags);
	unlock_kernel();
	up(&inode->i_sem);
	return error;
}

ssize_t
vfs_getxattr(struct dentry *dentry, char *name, void *value, size_t size)
{
	struct inode *inode = dentry->d_inode;
	int error;

	if (!inode->i_op->getxattr)
		return -EOPNOTSUPP;

	error = xattr_permission(inode, name, MAY_READ);
	if (error)
		return error;

	down(&inode->i_sem);
	lock_kernel();
	error = inode->i_op->getxattr(dentry, name, value, size);
	unlock_kernel();
	up(&inode->i_sem);
	return error;
}

int
vfs_removexattr(struct dentry *dentry, char *name)
{
	struct inode *inode = dentry->d_inode;
	int error;

	if (!inode->i_op->removexattr)
		return -EOPNOTSUPP;

	error = xattr_permission(inode, name, MAY_WRITE);
	if (error)
		return error;

	down(&inode->i_sem);
	lock_kernel();
	error = inode->i_op->removexattr(dentry, name);
	unlock_kernel();
	up(&inode->i_sem);

	return error;
}


/*
 * Extended attribute SET operations
 */
static long
setxattr(struct dentry *d, char *name, void *value, size_t size, int flags)
{
	int error;
	void *kvalue = NULL;
	char kname[XATTR_NAME_MAX + 1];

	if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
		return -EINVAL;

	error = strncpy_from_user(kname, name, sizeof(kname));
	if (error == 0 || error == sizeof(kname))
		error = -ERANGE;
	if (error < 0)
		return error;

	if (size) {
		if (size > XATTR_SIZE_MAX)
			return -E2BIG;
		kvalue = kmalloc(size, GFP_KERNEL);
		if (!kvalue)
			return -ENOMEM;
		if (copy_from_user(kvalue, value, size)) {
			kfree(kvalue);
			return -EFAULT;
		}
	}

	error = vfs_setxattr(d, kname, kvalue, size, flags);
	kfree(kvalue);
	return error;
}

asmlinkage long
sys_setxattr(char *path, char *name, void *value, size_t size, int flags)
{
	struct nameidata nd;
	int error;

	error = user_path_walk(path, &nd);
	if (error)
		return error;
	error = setxattr(nd.dentry, name, value, size, flags);
	path_release(&nd);
	return error;
}

asmlinkage long
sys_lsetxattr(char *path, char *name, void *value, size_t size, int flags)
{
	struct nameidata nd;
	int error;

	error = user_path_walk_link(path, &nd);
	if (error)
		return error;
	error = setxattr(nd.dentry, name, value, size, flags);
	path_release(&nd);
	return error;
}

asmlinkage long
sys_fsetxattr(int fd, char *name, void *value, size_t size, int flags)
{
	struct file *f;
	int error = -EBADF;

	f = fget(fd);
	if (!f)
		return error;
	error = setxattr(f->f_dentry, name, value, size, flags);
	fput(f);
	return error;
}

/*
 * Extended attribute GET operations
 */
static ssize_t
getxattr(struct dentry *d, char *name, void *value, size_t size)
{
	ssize_t error;
	void *kvalue = NULL;
	char kname[XATTR_NAME_MAX + 1];

	error = strncpy_from_user(kname, name, sizeof(kname));
	if (error == 0 || error == sizeof(kname))
		error = -ERANGE;
	if (error < 0)
		return error;

	if (size) {
		if (size > XATTR_SIZE_MAX)
			size = XATTR_SIZE_MAX;
		kvalue = kmalloc(size, GFP_KERNEL);
		if (!kvalue)
			return -ENOMEM;
		memset(kvalue, 0, size);
	}

	error = vfs_getxattr(d, kname, kvalue, size);
	if (error > 0) {
		if (size && copy_to_user(value, kvalue, error))
			error = -EFAULT;
	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
		/* The file system tried to returned a value bigger
		   than XATTR_SIZE_MAX bytes. Not possible. */
		error = -E2BIG;
	}
	kfree(kvalue);
	return error;
}

asmlinkage ssize_t
sys_getxattr(char *path, char *name, void *value, size_t size)
{
	struct nameidata nd;
	ssize_t error;

	error = user_path_walk(path, &nd);
	if (error)
		return error;
	error = getxattr(nd.dentry, name, value, size);
	path_release(&nd);
	return error;
}

asmlinkage ssize_t
sys_lgetxattr(char *path, char *name, void *value, size_t size)
{
	struct nameidata nd;
	ssize_t error;

	error = user_path_walk_link(path, &nd);
	if (error)
		return error;
	error = getxattr(nd.dentry, name, value, size);
	path_release(&nd);
	return error;
}

asmlinkage ssize_t
sys_fgetxattr(int fd, char *name, void *value, size_t size)
{
	struct file *f;
	ssize_t error = -EBADF;

	f = fget(fd);
	if (!f)
		return error;
	error = getxattr(f->f_dentry, name, value, size);
	fput(f);
	return error;
}

/*
 * Extended attribute LIST operations
 */
static ssize_t
listxattr(struct dentry *d, char *list, size_t size)
{
	ssize_t error;
	char *klist = NULL;

	if (size) {
		if (size > XATTR_LIST_MAX)
			size = XATTR_LIST_MAX;
		klist = kmalloc(size, GFP_KERNEL);
		if (!klist)
			return -ENOMEM;
	}

	error = -EOPNOTSUPP;
	if (d->d_inode->i_op && d->d_inode->i_op->listxattr) {
		lock_kernel();
		down(&d->d_inode->i_sem);
		error = d->d_inode->i_op->listxattr(d, klist, size);
		unlock_kernel();
		up(&d->d_inode->i_sem);
	}
	if (error > 0) {
		if (size && copy_to_user(list, klist, error))
			error = -EFAULT;
	} else if (error == -ERANGE && size >= XATTR_LIST_MAX) {
		/* The file system tried to returned a list bigger
		   than XATTR_LIST_MAX bytes. Not possible. */
		error = -E2BIG;
	}

	kfree(klist);
	return error;
}

asmlinkage ssize_t
sys_listxattr(char *path, char *list, size_t size)
{
	struct nameidata nd;
	ssize_t error;

	error = user_path_walk(path, &nd);
	if (error)
		return error;
	error = listxattr(nd.dentry, list, size);
	path_release(&nd);
	return error;
}

asmlinkage ssize_t
sys_llistxattr(char *path, char *list, size_t size)
{
	struct nameidata nd;
	ssize_t error;

	error = user_path_walk_link(path, &nd);
	if (error)
		return error;
	error = listxattr(nd.dentry, list, size);
	path_release(&nd);
	return error;
}

asmlinkage ssize_t
sys_flistxattr(int fd, char *list, size_t size)
{
	struct file *f;
	ssize_t error = -EBADF;

	f = fget(fd);
	if (!f)
		return error;
	error = listxattr(f->f_dentry, list, size);
	fput(f);
	return error;
}

/*
 * Extended attribute REMOVE operations
 */
static long
removexattr(struct dentry *d, char *name)
{
	int error;
	char kname[XATTR_NAME_MAX + 1];

	error = strncpy_from_user(kname, name, sizeof(kname));
	if (error == 0 || error == sizeof(kname))
		error = -ERANGE;
	if (error < 0)
		return error;

	return vfs_removexattr(d, kname);
}

asmlinkage long
sys_removexattr(char *path, char *name)
{
	struct nameidata nd;
	int error;

	error = user_path_walk(path, &nd);
	if (error)
		return error;
	error = removexattr(nd.dentry, name);
	path_release(&nd);
	return error;
}

asmlinkage long
sys_lremovexattr(char *path, char *name)
{
	struct nameidata nd;
	int error;

	error = user_path_walk_link(path, &nd);
	if (error)
		return error;
	error = removexattr(nd.dentry, name);
	path_release(&nd);
	return error;
}

asmlinkage long
sys_fremovexattr(int fd, char *name)
{
	struct file *f;
	int error = -EBADF;

	f = fget(fd);
	if (!f)
		return error;
	error = removexattr(f->f_dentry, name);
	fput(f);
	return error;
}