From: Kees Cook <keescook@chromium.org>
To: Christian Brauner <christian@brauner.io>
Cc: LKML <linux-kernel@vger.kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"Luis R. Rodriguez" <mcgrof@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Joe Lawrence <joe.lawrence@redhat.com>,
Waiman Long <longman@redhat.com>,
Dominik Brodowski <linux@dominikbrodowski.net>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v1 1/2] sysctl: cap to ULONG_MAX in proc_get_long()
Date: Mon, 15 Oct 2018 09:18:40 -0700 [thread overview]
Message-ID: <CAGXu5j+BZsmRXwXfXk1YcyuSRNMmre=K55e1CXaLJDUZ07rmvQ@mail.gmail.com> (raw)
In-Reply-To: <20181015105544.4395-2-christian@brauner.io>
On Mon, Oct 15, 2018 at 3:55 AM, Christian Brauner <christian@brauner.io> wrote:
> proc_get_long() is a funny function. It uses simple_strtoul() and for a
> good reason. proc_get_long() wants to always succeed the parse and return
> the maybe incorrect value and the trailing characters to check against a
> pre-defined list of acceptable trailing values.
> However, simple_strtoul() explicitly ignores overflows which can cause
What depends on simple_strtoul() ignoring overflows? Can we just cap
it to ULONG_MAX instead?
I note that both simple_strtoul() and simple_strtoull() are marked as
obsolete (more below).
> funny things like the following to happen:
>
> echo 18446744073709551616 > /proc/sys/fs/file-max
> cat /proc/sys/fs/file-max
> 0
>
> (Which will cause your system to silently die behind your back.)
>
> On the other hand kstrtoul() does do overflow detection but fails the parse
> in this case, does not return the trailing characters, and also fails the
> parse when anything other than '\n' is a trailing character whereas
> proc_get_long() wants to be more lenient.
This parsing strictness difference makes it seem like the simple_*()
shouldn't be considered obsolete...
and it's still very heavily used:
$ git grep -E 'simple_strtoull?\(' | wc -l
745
> Now, before adding another kstrtoul() function let's simply add a static
> parse strtoul_cap_erange() which does:
> - returns ULONG_MAX on ERANGE
> - returns the trailing characters to the caller
> This guarantees that we don't regress userspace in any way but also caps
> any parsed value to ULONG_MAX and prevents things like file-max to become 0
> on overflow.
-Kees
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2018-10-15 16:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 10:55 [PATCH v1 0/2] sysctl: cap file-max value at ULONG_MAX Christian Brauner
2018-10-15 10:55 ` [PATCH v1 1/2] sysctl: cap to ULONG_MAX in proc_get_long() Christian Brauner
2018-10-15 16:18 ` Kees Cook [this message]
2018-10-15 16:30 ` Christian Brauner
2018-10-15 19:01 ` Christian Brauner
2018-10-15 10:55 ` [PATCH v1 2/2] sysctl: handle overflow for file-max Christian Brauner
2018-10-15 16:11 ` Kees Cook
2018-10-15 16:28 ` Christian Brauner
2018-10-15 21:20 ` Kees Cook
2018-10-16 13:16 ` Christian Brauner
2018-10-16 14:38 ` Christian Brauner
2018-10-16 15:13 ` Waiman Long
2018-10-16 15:21 ` Christian Brauner
2018-10-16 15:25 ` Waiman Long
2018-10-16 15:29 ` Christian Brauner
2018-10-16 15:33 ` Christian Brauner
2018-10-16 15:34 ` Waiman Long
2018-10-16 15:40 ` Christian Brauner
2018-10-16 15:44 ` Waiman Long
2018-10-16 15:47 ` Christian Brauner
2018-10-16 15:53 ` Waiman Long
2018-10-16 15:59 ` Christian Brauner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAGXu5j+BZsmRXwXfXk1YcyuSRNMmre=K55e1CXaLJDUZ07rmvQ@mail.gmail.com' \
--to=keescook@chromium.org \
--cc=akpm@linux-foundation.org \
--cc=christian@brauner.io \
--cc=ebiederm@xmission.com \
--cc=joe.lawrence@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@dominikbrodowski.net \
--cc=longman@redhat.com \
--cc=mcgrof@kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).