Quoting Stefan Berger (Stefan Bergerstefanb@xxxxxxxxxxxxxxxxxx):
> +/*
> + * xattr_list_userns_rewrite - Rewrite list of xattr names for user namespaces
> + * or determine needed size for attribute list
> + * in case size == 0
> + *
> + * In a user namespace we do not present all extended attributes to the
> + * user. We filter out those that are in the list of userns supported xattr.
> + * Besides that we filter out those with @uid=<uid> when there is no mapping
> + * for that uid in the current user namespace.
> + *
> + * @list: list of 0-byte separated xattr names
> + * @size: the size of the list; may be 0 to determine needed list size
> + * @list_maxlen: allocated buffer size of list
> + */
> +static ssize_t
> +xattr_list_userns_rewrite(char *list, ssize_t size, size_t list_maxlen)
> +{
> + char *nlist = NULL;
> + size_t s_off, len, nlen;
> + ssize_t d_off;
> + char *name, *newname;
> +
> + if (!list || size < 0 || current_user_ns() == &init_user_ns)
> + return size;
> +
> + if (size) {
> + nlist = kmalloc(list_maxlen, GFP_KERNEL);
> + if (!nlist)
> + return -ENOMEM;
> + }
> +
> + s_off = d_off = 0;
> + while (s_off < size || size == 0) {
> + name = &list[s_off];
> +
> + len = strlen(name);
> + if (!len)
> + break;
> +
> + if (xattr_is_userns_supported(name, false) >= 0)
> + newname = name;
> + else {
> + newname = xattr_rewrite_userns_xattr(name);
Why are you doing this here? If we get here it means that
xattr_is_userns_supported() returned < 0, meaning name is
not userns-supported. So xattr_rewrite_userns_xattr() will
just return name. Am I missing something?
> + if (IS_ERR(newname)) {
> + d_off = PTR_ERR(newname);
> + goto out_free;
> + }
> + }
> + if (newname && !xattr_list_contains(nlist, d_off, newname)) {
Now here, if name was recalculated to @newname, and @newname is
found in the nlist, that should raise an error right? Something
fishy is going on?
> + nlen = strlen(newname);
> +
> + if (nlist) {
> + if (nlen + 1 > list_maxlen)
d_off needs to be set to -ERANGE here.
> + break;
> + strcpy(&nlist[d_off], newname);
> + }
> +
> + d_off += nlen + 1;
> + if (newname != name)
> + kfree(newname);
> + }
> + s_off += len + 1;
> + }
> + if (nlist)
> + memcpy(list, nlist, d_off);
> +out_free:
> + kfree(nlist);
> +
> + return d_off;
> +}
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