On Tue, Jul 31, 2018 at 6:51 PM Al Viro <v...@zeniv.linux.org.uk> wrote:
>
> On Tue, Jul 31, 2018 at 06:10:27PM +0200, Jann Horn wrote:
> > +/*
> > + * Most filesystems don't filter out bogus directory entry names, and
> > userspace
> > + * can get very confused by such names. Behave as if a low-level IO error
> > had
> > + * happened while reading directory entries.
> > + */
> > +bool bogus_dirent_name(int *errp, const char *name, int namlen,
> > + const char *caller)
> > +{
> > + if (namlen == 0) {
> > + pr_err_once("%s: filesystem returned bogus empty name\n",
> > + caller);
> > + *errp = -EUCLEAN;
> > + return true;
> > + }
> > + if (memchr(name, '/', namlen)) {
> > + pr_err_once("%s: filesystem returned bogus name '%*pEhp'
> > (contains slash)\n",
> > + caller, namlen, name);
> > + *errp = -EUCLEAN;
> > + return true;
> > + }
> > + return false;
> > +}
>
> > + if (bogus_dirent_name(&buf->result, name, namlen, __func__))
> > + return -EUCLEAN;
>
> These calling conventions st^Ware rather suboptimal. First of all,
> * none of ->actor() callbacks will ever get called directly.
> * there are only 4 callers. 3 of them (all in fs.h) are
> of the form return ....->actor(...) == 0; The fourth is
> return orig_ctx->actor(orig_ctx, name, namelen, offset, ino, d_type);
> in ovl_fill_real(), which itself is an ->actor() callback.
>
> So all these "return -E..." in the instances are completely pointless;
> we should just turn filldir_t into pointer-to-function-returning-bool
> and get rid of that boilerplate, rather than adding more to it.
Do you want me to try to write a patch that does that change?
> Furthermore, who the hell cares which callback has stepped into it?
> "The first time it happened from getdents(2) in a 32bit process and
> that's all you'll ever get out of me" seems to be less than helpful...
Yeah, true. Should I just remove the method name from the pr_err_once?
Or should I also use one of the _ratelimited things and print multiple
messages?
> And frankly, I would prefer
> buf->result = check_dirent_name(name, namelen);
> if (unlikely(buf->result))
> return false;
> making that thing return -EUCLEAN or 0. Quite possibly - inlining it
> as well...
I guess that would conform to normal kernel coding standards a bit better.
Thanks for the quick feedback!
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