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From: Aleksa Sarai <cyphar@cyphar.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: linux-ia64@vger.kernel.org, linux-sh@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Alexei Starovoitov <ast@kernel.org>,
	linux-kernel@vger.kernel.org, David Howells <dhowells@redhat.com>,
	linux-kselftest@vger.kernel.org, sparclinux@vger.kernel.org,
	Shuah Khan <shuah@kernel.org>,
	linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
	Tycho Andersen <tycho@tycho.ws>, Aleksa Sarai <asarai@suse.de>,
	Jiri Olsa <jolsa@redhat.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
	linux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
	Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
	linuxppc-dev@lists.ozlabs.org, linux-m68k@lists.linux-m68k.org,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Namhyung Kim <namhyung@kernel.org>,
	David Drysdale <drysdale@google.com>,
	Christian Brauner <christian@brauner.io>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	linux-parisc@vger.kernel.org, linux-api@vger.kernel.org,
	Chanho Min <chanho.min@lge.com>, Jeff Layton <jlayton@kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Eric Biederman <ebiederm@xmission.com>,
	linux-alpha@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	containers@lists.linux-foundation.org
Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers
Date: Thu, 5 Sep 2019 23:40:17 +1000
Message-ID: <20190905134017.rstiqa6v6roslzlu@yavin.dot.cyphar.com> (raw)
In-Reply-To: <20190905110544.d6c5t7rx25kvywmi@wittgenstein>

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On 2019-09-05, Christian Brauner <christian.brauner@ubuntu.com> wrote:
> On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote:
> > A common pattern for syscall extensions is increasing the size of a
> > struct passed from userspace, such that the zero-value of the new fields
> > result in the old kernel behaviour (allowing for a mix of userspace and
> > kernel vintages to operate on one another in most cases). This is done
> > in both directions -- hence two helpers -- though it's more common to
> > have to copy user space structs into kernel space.
> > 
> > Previously there was no common lib/ function that implemented
> > the necessary extension-checking semantics (and different syscalls
> > implemented them slightly differently or incompletely[1]). A future
> > patch replaces all of the common uses of this pattern to use the new
> > copy_struct_{to,from}_user() helpers.
> > 
> > [1]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
> >      similar checks to copy_struct_from_user() while rt_sigprocmask(2)
> >      always rejects differently-sized struct arguments.
> > 
> > Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> > Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

[...]

> > +	if (unlikely(!access_ok(src, usize)))
> > +		return -EFAULT;
> > +
> > +	/* Deal with trailing bytes. */
> > +	if (usize < ksize)
> > +		memset(dst + size, 0, rest);
[...]
> That's a change in behavior for clone3() and sched at least, no? Unless
> - which I guess you might have done - you have moved the "error out when
> the struct is too small" part before the call to copy_struct_from_user()
> for them.

Yes, I've put the minimum size check to the callers in all of the
cases (in the case of clone3() I've #define'd a CLONE_ARGS_SIZE_VER0 to
match the others -- see patch 2 of the series).

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  parent reply index

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-04 20:19 [PATCH v12 00/12] namei: openat2(2) path resolution restrictions Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Aleksa Sarai
2019-09-04 20:48   ` [PATCH v12 01/12] lib: introduce copy_struct_{to, from}_user helpers Linus Torvalds
2019-09-04 21:00   ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Randy Dunlap
2019-09-05  7:32   ` Peter Zijlstra
2019-09-05  9:26     ` Aleksa Sarai
2019-09-05  9:43       ` Peter Zijlstra
2019-09-05 10:57         ` Peter Zijlstra
2019-09-11 10:37           ` Aleksa Sarai
2019-09-05 13:35         ` Aleksa Sarai
2019-09-05 17:01         ` Aleksa Sarai
2019-09-05  8:43   ` Rasmus Villemoes
2019-09-05  9:50     ` Aleksa Sarai
2019-09-05 10:45       ` Christian Brauner
2019-09-05  9:09   ` [PATCH v12 01/12] lib: introduce copy_struct_{to, from}_user helpers Andreas Schwab
2019-09-05 10:13     ` Gabriel Paubert
2019-09-05 11:05   ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Christian Brauner
2019-09-05 11:17     ` Rasmus Villemoes
2019-09-05 11:29       ` Christian Brauner
2019-09-05 13:40     ` Aleksa Sarai [this message]
2019-09-05 11:09   ` Christian Brauner
2019-09-05 11:27     ` Aleksa Sarai
2019-09-05 11:40       ` Christian Brauner
2019-09-05 18:07   ` Al Viro
2019-09-05 18:23     ` Christian Brauner
2019-09-05 18:28       ` Al Viro
2019-09-05 18:35         ` Christian Brauner
2019-09-05 19:56         ` Aleksa Sarai
2019-09-05 22:31           ` Al Viro
2019-09-06  7:00           ` Christian Brauner
2019-09-05 23:00     ` Aleksa Sarai
2019-09-05 23:49       ` Al Viro
2019-09-06  0:09         ` Aleksa Sarai
2019-09-06  0:14         ` Al Viro
2019-09-04 20:19 ` [PATCH v12 02/12] clone3: switch to copy_struct_from_user() Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 03/12] sched_setattr: switch to copy_struct_{to, from}_user() Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 04/12] perf_event_open: switch to copy_struct_from_user() Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 05/12] namei: obey trailing magic-link DAC permissions Aleksa Sarai
2019-09-17 21:30   ` Jann Horn
2019-09-18 13:51     ` Aleksa Sarai
2019-09-18 15:46       ` Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 06/12] procfs: switch magic-link modes to be more sane Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 07/12] open: O_EMPTYPATH: procfs-less file descriptor re-opening Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 08/12] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 09/12] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 10/12] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-09-04 21:09   ` Linus Torvalds
2019-09-04 21:35     ` Linus Torvalds
2019-09-04 21:36       ` Linus Torvalds
2019-09-04 21:48     ` Aleksa Sarai
2019-09-04 22:16       ` Linus Torvalds
2019-09-04 22:31       ` David Howells
2019-09-04 22:38         ` Linus Torvalds
2019-09-04 23:29           ` Al Viro
2019-09-04 23:44             ` Linus Torvalds
2019-09-04 20:19 ` [PATCH v12 11/12] open: openat2(2) syscall Aleksa Sarai
2019-09-04 21:00   ` Randy Dunlap
2019-09-07 12:40   ` Jeff Layton
2019-09-07 16:58     ` Linus Torvalds
2019-09-07 17:42       ` Andy Lutomirski
2019-09-07 17:45         ` Linus Torvalds
2019-09-07 18:15           ` Andy Lutomirski
2019-09-10  6:35           ` Ingo Molnar
2019-09-08 16:24     ` Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 12/12] selftests: add openat2(2) selftests Aleksa Sarai

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