On Mon, Aug 30, 2021 at 9:59 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Mon, Aug 30, 2021 at 09:16:14AM -0700, Suren Baghdasaryan wrote:
> > On Mon, Aug 30, 2021 at 1:12 AM Rasmus Villemoes
> > <linux@xxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On 28/08/2021 23.47, Suren Baghdasaryan wrote:
> > > > On Fri, Aug 27, 2021 at 10:52 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > > >>
> > > >>>> + case PR_SET_VMA_ANON_NAME:
> > > >>>> + name = strndup_user((const char __user *)arg,
> > > >>>> + ANON_VMA_NAME_MAX_LEN);
> > > >>>> +
> > > >>>> + if (IS_ERR(name))
> > > >>>> + return PTR_ERR(name);
> > > >>>> +
> > > >>>> + for (pch = name; *pch != '\0'; pch++) {
> > > >>>> + if (!isprint(*pch)) {
> > > >>>> + kfree(name);
> > > >>>> + return -EINVAL;
> > > >>>
> > > >>> I think isprint() is too weak a check. For example, I would suggest
> > > >>> forbidding the following characters: ':', ']', '[', ' '. Perhaps
> > >
> > > Indeed. There's also the issue that the kernel's ctype actually
> > > implements some almost-but-not-quite latin1, so (some) chars above 0x7f
> > > would also pass isprint() - while everybody today expects utf-8, so the
> > > ability to put almost arbitrary sequences of chars with the high bit set
> > > could certainly confuse some parsers. IOW, don't use isprint() at all,
> > > just explicitly check for the byte values that we and up agreeing to
> > > allow/forbid.
> > >
> > > >>> isalnum() would be better? (permit a-zA-Z0-9) I wouldn't necessarily
> > > >>> be opposed to some punctuation characters, but let's avoid creating
> > > >>> confusion. Do you happen to know which characters are actually in use
> > > >>> today?
> > > >>
> > > >> There's some sense in refusing [, ], and :, but removing " " seems
> > > >> unhelpful for reasonable descriptors. As long as weird stuff is escaped,
> > > >> I think it's fine. Any parser can just extract with m|\[anon:(.*)\]$|
> > > >
> > > > I see no issue in forbidding '[' and ']' but whitespace and ':' are
> > > > currently used by Android. Would forbidding or escaping '[' and ']' be
> > > > enough?
> > >
> > > how about allowing [0x20, 0x7e] except [0x5b, 0x5d], i.e. all printable
> > > (including space) ascii characters, except [ \ ] - the brackets as
> > > already discussed, and backslash because then there's nobody who can get
> > > confused about whether there's some (and then which?) escaping mechanism
> > > in play - "\n" is simply never going to appear. Simple rules, easy to
> > > implement, easy to explain in a man page.
> >
> > Thanks for the suggestion, Rasmus. I'm all for keeping it simple.
> > Kees, Matthew, would that be acceptable?
>
> Yes, I think so. It permits all kinds of characters that might
> be confusing if passed on to something else, but we can't prohibit
> everything, and forbidding just these three should remove any confusion
> for any parser of /proc. Little Bobby Tables thanks you.
Thanks for all the feedback! I think I have enough change suggestions
to resping the next revision. Will send an update later today.
