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

[Dr. David Alan Gilbert]

* Vivek Goyal (vgoyal@redhat.com) wrote:
> 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.

It blocked user.virtiofs. more generically:

+        /* 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);

i.e. hides 'trusted.'

+        /* 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);

i.e. blocks client from 'user.virtiofs.'

Note, that is a problem for nesting, since having that at L1 means it
stops L2 from settings user.virtiofs.trusted.something (which it wants
to become user.virtiofs.user.virtiofs.trusted.something).

Using :map::user.virtiofs.:  works nicely for nesting (I've just tried
it), since that nests everything.

> 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."

No, the existing core option parser we're using overrides on subsequent
entries; so that would ignore the first -o xattrmap=

Dave

> 
> 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
> > 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK