linux-kernel - Re: [PATCH v8 2/3] mm: add a field to store names for private anonymous memory

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Message-ID: <CAJuCfpEWc+eTLYp_Xf9exMJCO_cFtvBUzi39+WbcSKZBXHe3SQ@mail.gmail.com>
Date:   Sat, 28 Aug 2021 14:47:46 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Colin Cross <ccross@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@...iv.linux.org.uk>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        Peter Xu <peterx@...hat.com>, rppt@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        vincenzo.frascino@....com,
        Chinwen Chang (張錦文) 
        <chinwen.chang@...iatek.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Jann Horn <jannh@...gle.com>, apopple@...dia.com,
        John Hubbard <jhubbard@...dia.com>,
        Yu Zhao <yuzhao@...gle.com>, Will Deacon <will@...nel.org>,
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        Hugh Dickins <hughd@...gle.com>, feng.tang@...el.com,
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        Muchun Song <songmuchun@...edance.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
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        linux@...musvillemoes.dk, LKML <linux-kernel@...r.kernel.org>,
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        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v8 2/3] mm: add a field to store names for private
 anonymous memory

On Fri, Aug 27, 2021 at 10:52 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Sat, Aug 28, 2021 at 02:47:03AM +0100, Matthew Wilcox wrote:
> > On Fri, Aug 27, 2021 at 12:18:57PM -0700, Suren Baghdasaryan wrote:
> > > +           anon_name = vma_anon_name(vma);
> > > +           if (anon_name) {
> > > +                   seq_pad(m, ' ');
> > > +                   seq_puts(m, "[anon:");
> > > +                   seq_write(m, anon_name, strlen(anon_name));
> > > +                   seq_putc(m, ']');
> > > +           }
>
> Maybe after seq_pad, use: seq_printf(m, "[anon:%s]", anon_name);

Good idea. Will change.

>
> >
> > ...
> >
> > > +   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
> > 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?

>
> For example, just escape it here instead of refusing to take it. Something
> like:
>
>         name = strndup_user((const char __user *)arg,
>                             ANON_VMA_NAME_MAX_LEN);
>         escaped = kasprintf(GFP_KERNEL, "%pE", name);

Did you mean "%*pE" as in
https://www.kernel.org/doc/html/latest/core-api/printk-formats.html#raw-buffer-as-an-escaped-string
?

>         if (escaped) {
>                 kfree(name);
>                 return -ENOMEM;
>         }
>         kfree(name);
>         name = escaped;
>
> --
> Kees Cook