Re: [PATCH v3 5/5] tools/virtiofsd: xattr name mappings: Simple 'map'

[Vivek Goyal]

On Wed, Oct 14, 2020 at 07:02:09PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> The mapping rule system implemented in the last few patches is
> extremely flexible, but not easy to use.  Add a simple
> 'map' type as a sprinkling of sugar to make it easy.
> 
> e.g.
> 
>   -o xattrmap=":map::user.virtiofs.:"
> 
> would be sufficient to prefix all xattr's
> or
> 
>   -o xattrmap=":map:trusted.:user.virtiofs.:"
> 
> would just prefix 'trusted.' xattr's and leave
> everything else alone.

Will it block "user.virtiofs.trusted." from client? As we discussed
that either we need to block it or we need to prefix it with another
user.virtiofs. I mean this rule alone is problematic and needs
to be coupled with more rules.

I am assuming one can specify multiple xattrmap on single line. So
one can also say.

-o xattrmap=":map:trusted.:user.virtiofs.:" -o 
xattrmap=":map:user.virtiofs.:user.virtiofs."

Thanks
Vivek

> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  docs/tools/virtiofsd.rst         |  18 ++++++
>  tools/virtiofsd/passthrough_ll.c | 108 ++++++++++++++++++++++++++++++-
>  2 files changed, 125 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
> index 5cb64612ed..e388ef253e 100644
> --- a/docs/tools/virtiofsd.rst
> +++ b/docs/tools/virtiofsd.rst
> @@ -127,6 +127,7 @@ Each rule consists of a number of fields separated with a 
> separator that is the
>  first non-white space character in the rule.  This separator must then be 
> used
>  for the whole rule.
>  White space may be added before and after each rule.
> +
>  Using ':' as the separator a rule is of the form:
>  
>  ``:type:scope:key:prepend:``
> @@ -162,6 +163,13 @@ on the server, and used as a new prefix.  It may be empty
>  in which case a 'server' rule will always match on all names from
>  the server.
>  
> +A simpler 'map' type provides a shorter syntax for the common case:
> +
> +``:map:key:prepend:``
> +
> +The 'map' type adds a number of separate rules to add **prepend** as a prefix
> +to the matched **key** (or all attributes if **key** is empty).
> +There may be at most one 'map' rule and it must be the last rule in the set.
>  
>  xattr-mapping Examples
>  ----------------------
> @@ -178,6 +186,11 @@ the first rule prefixes and strips 'user.virtiofs.',
>  the second rule hides any non-prefixed attributes that
>  the host set.
>  
> +This is equivalent to the 'map' rule:
> +
> +::
> +-o xattrmap=":map::user.virtiofs.:"
> +
>  2) Prefix 'trusted.' attributes, allow others through
>  
>  ::
> @@ -200,6 +213,11 @@ the 'user.viritofs.' path directly.
>  Finally, the fourth rule lets all remaining attributes
>  through.
>  
> +This is equivalent to the 'map' rule:
> +
> +::
> +-o xattrmap="/map/trusted./user.virtiofs./"
> +
>  3) Hide 'security.' attributes, and allow everything else
>  
>  ::
> diff --git a/tools/virtiofsd/passthrough_ll.c 
> b/tools/virtiofsd/passthrough_ll.c
> index 8406a2ae86..a1b3364ba3 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -2074,6 +2074,106 @@ static void free_xattrmap(XattrMapEntry *map)
>      g_free(map);
>  }
>  
> +/*
> + * Handle the 'map' type, which is sugar for a set of commands
> + * for the common case of prefixing a subset or everything,
> + * and allowing anything not prefixed through.
> + * It must be the last entry in the stream, although there
> + * can be other entries before it.
> + * The form is:
> + *    :map:key:prefix:
> + *
> + * key maybe empty in which case all entries are prefixed.
> + */
> +static XattrMapEntry *parse_xattrmap_map(const char *rule,
> +                                         XattrMapEntry *map,
> +                                         size_t *nentries)
> +{
> +    char sep = *rule++;
> +    const char *tmp;
> +    char *key;
> +    char *prefix;
> +    XattrMapEntry tmp_entry;
> +
> +    /* At start of 'key' field */
> +    tmp = strchr(rule, sep);
> +    if (!tmp) {
> +        fuse_log(FUSE_LOG_ERR,
> +                 "%s: Missing '%c' at end of key field in map rule\n",
> +                 __func__, sep);
> +        exit(1);
> +    }
> +
> +    key = g_strndup(rule, tmp - rule);
> +    rule = tmp + 1;
> +
> +    /* At start of prefix field */
> +    tmp = strchr(rule, sep);
> +    if (!tmp) {
> +        fuse_log(FUSE_LOG_ERR,
> +                 "%s: Missing '%c' at end of prefix field in map rule\n",
> +                 __func__, sep);
> +        exit(1);
> +    }
> +
> +    prefix = g_strndup(rule, tmp - rule);
> +    rule = tmp + 1;
> +
> +    /*
> +     * This should be the end of the string, we don't allow
> +     * any more commands after 'map'.
> +     */
> +    if (*rule) {
> +        fuse_log(FUSE_LOG_ERR,
> +                 "%s: Expecting end of command after map, found '%c'\n",
> +                 __func__, *rule);
> +        exit(1);
> +    }
> +
> +    /* 1st: Prefix matches/everything */
> +    tmp_entry.flags = XATTR_MAP_FLAG_PREFIX | XATTR_MAP_FLAG_ALL;
> +    tmp_entry.key = g_strdup(key);
> +    tmp_entry.prepend = g_strdup(prefix);
> +    map = add_xattrmap_entry(map, nentries, &tmp_entry);
> +
> +    if (!*key) {
> +        /* Prefix all case */
> +
> +        /* 2nd: Hide any non-prefixed entries on the host */
> +        tmp_entry.flags = XATTR_MAP_FLAG_END_BAD | XATTR_MAP_FLAG_ALL |
> +                          XATTR_MAP_FLAG_LAST;
> +        tmp_entry.key = g_strdup("");
> +        tmp_entry.prepend = g_strdup("");
> +        map = add_xattrmap_entry(map, nentries, &tmp_entry);
> +    } else {
> +        /* Prefix matching case */
> +
> +        /* 2nd: Hide non-prefixed but matching entries on the host */
> +        tmp_entry.flags = XATTR_MAP_FLAG_END_BAD | XATTR_MAP_FLAG_SERVER;
> +        tmp_entry.key = g_strdup(""); /* Not used */
> +        tmp_entry.prepend = g_strdup(key);
> +        map = add_xattrmap_entry(map, nentries, &tmp_entry);
> +
> +        /* 3rd: Stop the client accessing prefixed attributes directly */
> +        tmp_entry.flags = XATTR_MAP_FLAG_END_BAD | XATTR_MAP_FLAG_CLIENT;
> +        tmp_entry.key = g_strdup(prefix);
> +        tmp_entry.prepend = g_strdup(""); /* Not used */
> +        map = add_xattrmap_entry(map, nentries, &tmp_entry);
> +
> +        /* 4th: Everything else is OK */
> +        tmp_entry.flags = XATTR_MAP_FLAG_END_OK | XATTR_MAP_FLAG_ALL |
> +                          XATTR_MAP_FLAG_LAST;
> +        tmp_entry.key = g_strdup("");
> +        tmp_entry.prepend = g_strdup("");
> +        map = add_xattrmap_entry(map, nentries, &tmp_entry);
> +    }
> +
> +    g_free(key);
> +    g_free(prefix);
> +
> +    return map;
> +}
> +
>  static XattrMapEntry *parse_xattrmap(struct lo_data *lo)
>  {
>      XattrMapEntry *res = NULL;
> @@ -2102,10 +2202,16 @@ static XattrMapEntry *parse_xattrmap(struct lo_data 
> *lo)
>              tmp_entry.flags |= XATTR_MAP_FLAG_END_OK;
>          } else if (strstart(map, "bad", &map)) {
>              tmp_entry.flags |= XATTR_MAP_FLAG_END_BAD;
> +        } else if (strstart(map, "map", &map)) {
> +            /*
> +             * map is sugar that adds a number of rules, and must be
> +             * the last entry.
> +             */
> +            return parse_xattrmap_map(map, res, &nentries);
>          } else {
>              fuse_log(FUSE_LOG_ERR,
>                       "%s: Unexpected type;"
> -                     "Expecting 'prefix', 'ok', or 'bad' in rule %zu\n",
> +                     "Expecting 'prefix', 'ok', 'bad' or 'map' in rule 
> %zu\n",
>                       __func__, nentries);
>              exit(1);
>          }
> -- 
> 2.28.0
>