On Fri, Jun 28, 2024 at 11:45:17AM GMT, Jan Kara wrote: > On Thu 27-06-24 19:26:24, Eric Sandeen wrote: > > Multiple filesystems take uid and gid as options, and the code to > > create the ID from an integer and validate it is standard boilerplate > > that can be moved into common helper functions, so do that for > > consistency and less cut&paste. > > > > This also helps avoid the buggy pattern noted by Seth Jenkins at > > https://lore.kernel.org/lkml/CALxfFW4BXhEwxR0Q5LSkg-8Vb4r2MONKCcUCVioehXQKr35eHg@xxxxxxxxxxxxxx/ > > because uid/gid parsing will fail before any assignment in most > > filesystems. > > > > Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxxx> > > I like the idea since this seems like a nobrainer but is actually > surprisingly subtle... > > > diff --git a/fs/fs_parser.c b/fs/fs_parser.c > > index a4d6ca0b8971..24727ec34e5a 100644 > > --- a/fs/fs_parser.c > > +++ b/fs/fs_parser.c > > @@ -308,6 +308,40 @@ int fs_param_is_fd(struct p_log *log, const struct fs_parameter_spec *p, > > } > > EXPORT_SYMBOL(fs_param_is_fd); > > > > +int fs_param_is_uid(struct p_log *log, const struct fs_parameter_spec *p, > > + struct fs_parameter *param, struct fs_parse_result *result) > > +{ > > + kuid_t uid; > > + > > + if (fs_param_is_u32(log, p, param, result) != 0) > > + return fs_param_bad_value(log, param); > > + > > + uid = make_kuid(current_user_ns(), result->uint_32); > > But here is the problem: Filesystems mountable in user namespaces need to use > fc->user_ns for resolving uids / gids (e.g. like fuse_parse_param()). > Having helpers that work for some filesystems and are subtly broken for > others is worse than no helpers... Or am I missing something? > > And the problem with fc->user_ns is that currently __fs_parse() does not > get fs_context as an argument... So that will need some larger work. Not really. If someone does an fsopen() in a namespace but the process that actually sets mount options is in another namespace then it's completely intransparent what uid/gid this will resolve to if it's resovled according to fsopen(). It's also a bit strange if someone ends up handing off a tmpfs fscontext that was created in the initial namespace to some random namespace and they now can set uid/gid options that aren't mapped according to their namespace but instead are 1:1 resolved according to the intial namespace. So this would hinder delegation. The expectation is that uid/gid options are resolved in the caller's namespace and that shouldn't be any different for fscontexts for namespace mountable filesystems. The crucial point is to ensure that the resulting kuid/kgid can be resolved in the namespace the filesystem is mounted in at the end. That's what was lacking in e.g., tmpfs in commit 0200679fc795 ("tmpfs: verify {g,u}id mount options correctly") The fuse conversion is the only inconsistency in that regard.
