// SPDX-License-Identifier: GPL-2.0-only
/*
  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>
  Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
 */
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/xattr.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/evm.h>
#include <linux/syscalls.h>
#include <linux/export.h>
#include <linux/fsnotify.h>
#include <linux/audit.h>
#include <linux/vmalloc.h>
#include <linux/posix_acl_xattr.h>

#include <linux/uaccess.h>

static const char *
strcmp_prefix(const char *a, const char *a_prefix)
{
        while (*a_prefix && *a == *a_prefix) {
                a++;
                a_prefix++;
        }
        return *a_prefix ? NULL : a;
}

/*
 * In order to implement different sets of xattr operations for each xattr
 * prefix, a filesystem should create a null-terminated array of struct
 * xattr_handler (one for each prefix) and hang a pointer to it off of the
 * s_xattr field of the superblock.
 */
#define for_each_xattr_handler(handlers, handler)               \
        if (handlers)                                           \
                for ((handler) = *(handlers)++;                 \
                        (handler) != NULL;                      \
                        (handler) = *(handlers)++)

/*
 * Find the xattr_handler with the matching prefix.
 */
static const struct xattr_handler *
xattr_resolve_name(struct inode *inode, const char **name)
{
        const struct xattr_handler **handlers = inode->i_sb->s_xattr;
        const struct xattr_handler *handler;

        if (!(inode->i_opflags & IOP_XATTR)) {
                if (unlikely(is_bad_inode(inode)))
                        return ERR_PTR(-EIO);
                return ERR_PTR(-EOPNOTSUPP);
        }
        for_each_xattr_handler(handlers, handler) {
                const char *n;

                n = strcmp_prefix(*name, xattr_prefix(handler));
                if (n) {
                        if (!handler->prefix ^ !*n) {
                                if (*n)
                                        continue;
                                return ERR_PTR(-EINVAL);
                        }
                        *name = n;
                        return handler;
                }
        }
        return ERR_PTR(-EOPNOTSUPP);
}

/*
 * 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_IMMUTABLE(inode) || IS_APPEND(inode))
                        return -EPERM;
                /*
                 * Updating an xattr will likely cause i_uid and i_gid
                 * to be writen back improperly if their true value is
                 * unknown to the vfs.
                 */
                if (HAS_UNMAPPED_ID(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 be accessed by privileged users.
         */
        if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN)) {
                if (!capable(CAP_SYS_ADMIN))
                        return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
                return 0;
        }

        /*
         * In the user.* namespace, only regular files and directories can have
         * extended attributes. For sticky directories, only the owner and
         * privileged users can write attributes.
         */
        if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN)) {
                if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
                        return (mask & MAY_WRITE) ? -EPERM : -ENODATA;
                if (S_ISDIR(inode->i_mode) && (inode->i_mode & S_ISVTX) &&
                    (mask & MAY_WRITE) && !inode_owner_or_capable(inode))
                        return -EPERM;
        }

        return inode_permission(inode, mask);
}

int
__vfs_setxattr(struct dentry *dentry, struct inode *inode, const char *name,
               const void *value, size_t size, int flags)
{
        const struct xattr_handler *handler;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->set)
                return -EOPNOTSUPP;
        if (size == 0)
                value = "";  /* empty EA, do not remove */
        return handler->set(handler, dentry, inode, name, value, size, flags);
}
EXPORT_SYMBOL(__vfs_setxattr);

/**
 *  __vfs_setxattr_noperm - perform setxattr operation without performing
 *  permission checks.
 *
 *  @dentry - object to perform setxattr on
 *  @name - xattr name to set
 *  @value - value to set @name to
 *  @size - size of @value
 *  @flags - flags to pass into filesystem operations
 *
 *  returns the result of the internal setxattr or setsecurity operations.
 *
 *  This function requires the caller to lock the inode's i_mutex before it
 *  is executed. It also assumes that the caller will make the appropriate
 *  permission checks.
 */
int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
                const void *value, size_t size, int flags)
{
        struct inode *inode = dentry->d_inode;
        int error = -EAGAIN;
        int issec = !strncmp(name, XATTR_SECURITY_PREFIX,
                                   XATTR_SECURITY_PREFIX_LEN);

        if (issec)
                inode->i_flags &= ~S_NOSEC;
        if (inode->i_opflags & IOP_XATTR) {
                error = __vfs_setxattr(dentry, inode, name, value, size, flags);
                if (!error) {
                        fsnotify_xattr(dentry);
                        security_inode_post_setxattr(dentry, name, value,
                                                     size, flags);
                }
        } else {
                if (unlikely(is_bad_inode(inode)))
                        return -EIO;
        }
        if (error == -EAGAIN) {
                error = -EOPNOTSUPP;

                if (issec) {
                        const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;

                        error = security_inode_setsecurity(inode, suffix, value,
                                                           size, flags);
                        if (!error)
                                fsnotify_xattr(dentry);
                }
        }

        return error;
}


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

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

        inode_lock(inode);
        error = security_inode_setxattr(dentry, name, value, size, flags);
        if (error)
                goto out;

        error = __vfs_setxattr_noperm(dentry, name, value, size, flags);

out:
        inode_unlock(inode);
        return error;
}
EXPORT_SYMBOL_GPL(vfs_setxattr);

static ssize_t
xattr_getsecurity(struct inode *inode, const char *name, void *value,
                        size_t size)
{
        void *buffer = NULL;
        ssize_t len;

        if (!value || !size) {
                len = security_inode_getsecurity(inode, name, &buffer, false);
                goto out_noalloc;
        }

        len = security_inode_getsecurity(inode, name, &buffer, true);
        if (len < 0)
                return len;
        if (size < len) {
                len = -ERANGE;
                goto out;
        }
        memcpy(value, buffer, len);
out:
        kfree(buffer);
out_noalloc:
        return len;
}

/*
 * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
 *
 * Allocate memory, if not already allocated, or re-allocate correct size,
 * before retrieving the extended attribute.
 *
 * Returns the result of alloc, if failed, or the getxattr operation.
 */
ssize_t
vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
                   size_t xattr_size, gfp_t flags)
{
        const struct xattr_handler *handler;
        struct inode *inode = dentry->d_inode;
        char *value = *xattr_value;
        int error;

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

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->get)
                return -EOPNOTSUPP;
        error = handler->get(handler, dentry, inode, name, NULL, 0);
        if (error < 0)
                return error;

        if (!value || (error > xattr_size)) {
                value = krealloc(*xattr_value, error + 1, flags);
                if (!value)
                        return -ENOMEM;
                memset(value, 0, error + 1);
        }

        error = handler->get(handler, dentry, inode, name, value, error);
        *xattr_value = value;
        return error;
}

ssize_t
__vfs_getxattr(struct dentry *dentry, struct inode *inode, const char *name,
               void *value, size_t size)
{
        const struct xattr_handler *handler;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->get)
                return -EOPNOTSUPP;
        return handler->get(handler, dentry, inode, name, value, size);
}
EXPORT_SYMBOL(__vfs_getxattr);

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

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

        error = security_inode_getxattr(dentry, name);
        if (error)
                return error;

        if (!strncmp(name, XATTR_SECURITY_PREFIX,
                                XATTR_SECURITY_PREFIX_LEN)) {
                const char *suffix = name + XATTR_SECURITY_PREFIX_LEN;
                int ret = xattr_getsecurity(inode, suffix, value, size);
                /*
                 * Only overwrite the return value if a security module
                 * is actually active.
                 */
                if (ret == -EOPNOTSUPP)
                        goto nolsm;
                return ret;
        }
nolsm:
        return __vfs_getxattr(dentry, inode, name, value, size);
}
EXPORT_SYMBOL_GPL(vfs_getxattr);

ssize_t
vfs_listxattr(struct dentry *dentry, char *list, size_t size)
{
        struct inode *inode = d_inode(dentry);
        ssize_t error;

        error = security_inode_listxattr(dentry);
        if (error)
                return error;
        if (inode->i_op->listxattr && (inode->i_opflags & IOP_XATTR)) {
                error = inode->i_op->listxattr(dentry, list, size);
        } else {
                error = security_inode_listsecurity(inode, list, size);
                if (size && error > size)
                        error = -ERANGE;
        }
        return error;
}
EXPORT_SYMBOL_GPL(vfs_listxattr);

int
__vfs_removexattr(struct dentry *dentry, const char *name)
{
        struct inode *inode = d_inode(dentry);
        const struct xattr_handler *handler;

        handler = xattr_resolve_name(inode, &name);
        if (IS_ERR(handler))
                return PTR_ERR(handler);
        if (!handler->set)
                return -EOPNOTSUPP;
        return handler->set(handler, dentry, inode, name, NULL, 0, XATTR_REPLACE);
}
EXPORT_SYMBOL(__vfs_removexattr);

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

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

        inode_lock(inode);
        error = security_inode_removexattr(dentry, name);
        if (error)
                goto out;

        error = __vfs_removexattr(dentry, name);

        if (!error) {
                fsnotify_xattr(dentry);
                evm_inode_post_removexattr(dentry, name);
        }

out:
        inode_unlock(inode);
        return error;
}
EXPORT_SYMBOL_GPL(vfs_removexattr);


/*
 * Extended attribute SET operations
 */
static long
setxattr(struct dentry *d, const char __user *name, const void __user *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 = kvmalloc(size, GFP_KERNEL);
                if (!kvalue)
                        return -ENOMEM;
                if (copy_from_user(kvalue, value, size)) {
                        error = -EFAULT;
                        goto out;
                }
                if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
                    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
                        posix_acl_fix_xattr_from_user(kvalue, size);
                else if (strcmp(kname, XATTR_NAME_CAPS) == 0) {
                        error = cap_convert_nscap(d, &kvalue, size);
                        if (error < 0)
                                goto out;
                        size = error;
                }
        }

        error = vfs_setxattr(d, kname, kvalue, size, flags);
out:
        kvfree(kvalue);

        return error;
}

static int path_setxattr(const char __user *pathname,
                         const char __user *name, const void __user *value,
                         size_t size, int flags, unsigned int lookup_flags)
{
        struct path path;
        int error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = mnt_want_write(path.mnt);
        if (!error) {
                error = setxattr(path.dentry, name, value, size, flags);
                mnt_drop_write(path.mnt);
        }
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE5(setxattr, const char __user *, pathname,
                const char __user *, name, const void __user *, value,
                size_t, size, int, flags)
{
        return path_setxattr(pathname, name, value, size, flags, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE5(lsetxattr, const char __user *, pathname,
                const char __user *, name, const void __user *, value,
                size_t, size, int, flags)
{
        return path_setxattr(pathname, name, value, size, flags, 0);
}

SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
                const void __user *,value, size_t, size, int, flags)
{
        struct fd f = fdget(fd);
        int error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = mnt_want_write_file(f.file);
        if (!error) {
                error = setxattr(f.file->f_path.dentry, name, value, size, flags);
                mnt_drop_write_file(f.file);
        }
        fdput(f);
        return error;
}

/*
 * Extended attribute GET operations
 */
static ssize_t
getxattr(struct dentry *d, const char __user *name, void __user *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 = kvzalloc(size, GFP_KERNEL);
                if (!kvalue)
                        return -ENOMEM;
        }

        error = vfs_getxattr(d, kname, kvalue, size);
        if (error > 0) {
                if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
                    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
                        posix_acl_fix_xattr_to_user(kvalue, error);
                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;
        }

        kvfree(kvalue);

        return error;
}

static ssize_t path_getxattr(const char __user *pathname,
                             const char __user *name, void __user *value,
                             size_t size, unsigned int lookup_flags)
{
        struct path path;
        ssize_t error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = getxattr(path.dentry, name, value, size);
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE4(getxattr, const char __user *, pathname,
                const char __user *, name, void __user *, value, size_t, size)
{
        return path_getxattr(pathname, name, value, size, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE4(lgetxattr, const char __user *, pathname,
                const char __user *, name, void __user *, value, size_t, size)
{
        return path_getxattr(pathname, name, value, size, 0);
}

SYSCALL_DEFINE4(fgetxattr, int, fd, const char __user *, name,
                void __user *, value, size_t, size)
{
        struct fd f = fdget(fd);
        ssize_t error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = getxattr(f.file->f_path.dentry, name, value, size);
        fdput(f);
        return error;
}

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

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

        error = vfs_listxattr(d, klist, size);
        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;
        }

        kvfree(klist);

        return error;
}

static ssize_t path_listxattr(const char __user *pathname, char __user *list,
                              size_t size, unsigned int lookup_flags)
{
        struct path path;
        ssize_t error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = listxattr(path.dentry, list, size);
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE3(listxattr, const char __user *, pathname, char __user *, list,
                size_t, size)
{
        return path_listxattr(pathname, list, size, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE3(llistxattr, const char __user *, pathname, char __user *, list,
                size_t, size)
{
        return path_listxattr(pathname, list, size, 0);
}

SYSCALL_DEFINE3(flistxattr, int, fd, char __user *, list, size_t, size)
{
        struct fd f = fdget(fd);
        ssize_t error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = listxattr(f.file->f_path.dentry, list, size);
        fdput(f);
        return error;
}

/*
 * Extended attribute REMOVE operations
 */
static long
removexattr(struct dentry *d, const char __user *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);
}

static int path_removexattr(const char __user *pathname,
                            const char __user *name, unsigned int lookup_flags)
{
        struct path path;
        int error;
retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (error)
                return error;
        error = mnt_want_write(path.mnt);
        if (!error) {
                error = removexattr(path.dentry, name);
                mnt_drop_write(path.mnt);
        }
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

SYSCALL_DEFINE2(removexattr, const char __user *, pathname,
                const char __user *, name)
{
        return path_removexattr(pathname, name, LOOKUP_FOLLOW);
}

SYSCALL_DEFINE2(lremovexattr, const char __user *, pathname,
                const char __user *, name)
{
        return path_removexattr(pathname, name, 0);
}

SYSCALL_DEFINE2(fremovexattr, int, fd, const char __user *, name)
{
        struct fd f = fdget(fd);
        int error = -EBADF;

        if (!f.file)
                return error;
        audit_file(f.file);
        error = mnt_want_write_file(f.file);
        if (!error) {
                error = removexattr(f.file->f_path.dentry, name);
                mnt_drop_write_file(f.file);
        }
        fdput(f);
        return error;
}

/*
 * Combine the results of the list() operation from every xattr_handler in the
 * list.
 */
ssize_t
generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
{
        const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
        unsigned int size = 0;

        if (!buffer) {
                for_each_xattr_handler(handlers, handler) {
                        if (!handler->name ||
                            (handler->list && !handler->list(dentry)))
                                continue;
                        size += strlen(handler->name) + 1;
                }
        } else {
                char *buf = buffer;
                size_t len;

                for_each_xattr_handler(handlers, handler) {
                        if (!handler->name ||
                            (handler->list && !handler->list(dentry)))
                                continue;
                        len = strlen(handler->name);
                        if (len + 1 > buffer_size)
                                return -ERANGE;
                        memcpy(buf, handler->name, len + 1);
                        buf += len + 1;
                        buffer_size -= len + 1;
                }
                size = buf - buffer;
        }
        return size;
}
EXPORT_SYMBOL(generic_listxattr);

/**
 * xattr_full_name  -  Compute full attribute name from suffix
 *
 * @handler:    handler of the xattr_handler operation
 * @name:       name passed to the xattr_handler operation
 *
 * The get and set xattr handler operations are called with the remainder of
 * the attribute name after skipping the handler's prefix: for example, "foo"
 * is passed to the get operation of a handler with prefix "user." to get
 * attribute "user.foo".  The full name is still "there" in the name though.
 *
 * Note: the list xattr handler operation when called from the vfs is passed a
 * NULL name; some file systems use this operation internally, with varying
 * semantics.
 */
const char *xattr_full_name(const struct xattr_handler *handler,
                            const char *name)
{
        size_t prefix_len = strlen(xattr_prefix(handler));

        return name - prefix_len;
}
EXPORT_SYMBOL(xattr_full_name);

/*
 * Allocate new xattr and copy in the value; but leave the name to callers.
 */
struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
{
        struct simple_xattr *new_xattr;
        size_t len;

        /* wrap around? */
        len = sizeof(*new_xattr) + size;
        if (len < sizeof(*new_xattr))
                return NULL;

        new_xattr = kmalloc(len, GFP_KERNEL);
        if (!new_xattr)
                return NULL;

        new_xattr->size = size;
        memcpy(new_xattr->value, value, size);
        return new_xattr;
}

/*
 * xattr GET operation for in-memory/pseudo filesystems
 */
int simple_xattr_get(struct simple_xattrs *xattrs, const char *name,
                     void *buffer, size_t size)
{
        struct simple_xattr *xattr;
        int ret = -ENODATA;

        spin_lock(&xattrs->lock);
        list_for_each_entry(xattr, &xattrs->head, list) {
                if (strcmp(name, xattr->name))
                        continue;

                ret = xattr->size;
                if (buffer) {
                        if (size < xattr->size)
                                ret = -ERANGE;
                        else
                                memcpy(buffer, xattr->value, xattr->size);
                }
                break;
        }
        spin_unlock(&xattrs->lock);
        return ret;
}

/**
 * simple_xattr_set - xattr SET operation for in-memory/pseudo filesystems
 * @xattrs: target simple_xattr list
 * @name: name of the extended attribute
 * @value: value of the xattr. If %NULL, will remove the attribute.
 * @size: size of the new xattr
 * @flags: %XATTR_{CREATE|REPLACE}
 *
 * %XATTR_CREATE is set, the xattr shouldn't exist already; otherwise fails
 * with -EEXIST.  If %XATTR_REPLACE is set, the xattr should exist;
 * otherwise, fails with -ENODATA.
 *
 * Returns 0 on success, -errno on failure.
 */
int simple_xattr_set(struct simple_xattrs *xattrs, const char *name,
                     const void *value, size_t size, int flags)
{
        struct simple_xattr *xattr;
        struct simple_xattr *new_xattr = NULL;
        int err = 0;

        /* value == NULL means remove */
        if (value) {
                new_xattr = simple_xattr_alloc(value, size);
                if (!new_xattr)
                        return -ENOMEM;

                new_xattr->name = kstrdup(name, GFP_KERNEL);
                if (!new_xattr->name) {
                        kfree(new_xattr);
                        return -ENOMEM;
                }
        }

        spin_lock(&xattrs->lock);
        list_for_each_entry(xattr, &xattrs->head, list) {
                if (!strcmp(name, xattr->name)) {
                        if (flags & XATTR_CREATE) {
                                xattr = new_xattr;
                                err = -EEXIST;
                        } else if (new_xattr) {
                                list_replace(&xattr->list, &new_xattr->list);
                        } else {
                                list_del(&xattr->list);
                        }
                        goto out;
                }
        }
        if (flags & XATTR_REPLACE) {
                xattr = new_xattr;
                err = -ENODATA;
        } else {
                list_add(&new_xattr->list, &xattrs->head);
                xattr = NULL;
        }
out:
        spin_unlock(&xattrs->lock);
        if (xattr) {
                kfree(xattr->name);
                kfree(xattr);
        }
        return err;

}

static bool xattr_is_trusted(const char *name)
{
        return !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN);
}

static int xattr_list_one(char **buffer, ssize_t *remaining_size,
                          const char *name)
{
        size_t len = strlen(name) + 1;
        if (*buffer) {
                if (*remaining_size < len)
                        return -ERANGE;
                memcpy(*buffer, name, len);
                *buffer += len;
        }
        *remaining_size -= len;
        return 0;
}

/*
 * xattr LIST operation for in-memory/pseudo filesystems
 */
ssize_t simple_xattr_list(struct inode *inode, struct simple_xattrs *xattrs,
                          char *buffer, size_t size)
{
        bool trusted = capable(CAP_SYS_ADMIN);
        struct simple_xattr *xattr;
        ssize_t remaining_size = size;
        int err = 0;

#ifdef CONFIG_FS_POSIX_ACL
        if (IS_POSIXACL(inode)) {
                if (inode->i_acl) {
                        err = xattr_list_one(&buffer, &remaining_size,
                                             XATTR_NAME_POSIX_ACL_ACCESS);
                        if (err)
                                return err;
                }
                if (inode->i_default_acl) {
                        err = xattr_list_one(&buffer, &remaining_size,
                                             XATTR_NAME_POSIX_ACL_DEFAULT);
                        if (err)
                                return err;
                }
        }
#endif

        spin_lock(&xattrs->lock);
        list_for_each_entry(xattr, &xattrs->head, list) {
                /* skip "trusted." attributes for unprivileged callers */
                if (!trusted && xattr_is_trusted(xattr->name))
                        continue;

                err = xattr_list_one(&buffer, &remaining_size, xattr->name);
                if (err)
                        break;
        }
        spin_unlock(&xattrs->lock);

        return err ? err : size - remaining_size;
}

/*
 * Adds an extended attribute to the list
 */
void simple_xattr_list_add(struct simple_xattrs *xattrs,
                           struct simple_xattr *new_xattr)
{
        spin_lock(&xattrs->lock);
        list_add(&new_xattr->list, &xattrs->head);
        spin_unlock(&xattrs->lock);
}