From: Peter Zijlstra <peterz@infradead.org>
To: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
Jeff Layton <jlayton@kernel.org>,
"J. Bruce Fields" <bfields@fieldses.org>,
Arnd Bergmann <arnd@arndb.de>,
David Howells <dhowells@redhat.com>,
Shuah Khan <shuah@kernel.org>,
Shuah Khan <skhan@linuxfoundation.org>,
Ingo Molnar <mingo@redhat.com>,
Christian Brauner <christian@brauner.io>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Eric Biederman <ebiederm@xmission.com>,
Andy Lutomirski <luto@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Alexei Starovoitov <ast@kernel.org>,
Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>,
Tycho Andersen <tycho@tycho.ws>,
David Drysdale <drysdale@google.com>,
Chanho Min <chanho.min@lge.com>, Oleg Nesterov <oleg@redhat.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Aleksa Sarai <asarai@suse.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
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patrick.bellasi@arm.com
Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers
Date: Thu, 5 Sep 2019 12:57:49 +0200 [thread overview]
Message-ID: <20190905105749.GW2386@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190905094305.GJ2349@hirez.programming.kicks-ass.net>
On Thu, Sep 05, 2019 at 11:43:05AM +0200, Peter Zijlstra wrote:
> On Thu, Sep 05, 2019 at 07:26:22PM +1000, Aleksa Sarai wrote:
> > On 2019-09-05, Peter Zijlstra <peterz@infradead.org> wrote:
> > > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote:
> > > > +/**
> > > > + * copy_struct_to_user: copy a struct to user space
> > > > + * @dst: Destination address, in user space.
> > > > + * @usize: Size of @dst struct.
> > > > + * @src: Source address, in kernel space.
> > > > + * @ksize: Size of @src struct.
> > > > + *
> > > > + * Copies a struct from kernel space to user space, in a way that guarantees
> > > > + * backwards-compatibility for struct syscall arguments (as long as future
> > > > + * struct extensions are made such that all new fields are *appended* to the
> > > > + * old struct, and zeroed-out new fields have the same meaning as the old
> > > > + * struct).
> > > > + *
> > > > + * @ksize is just sizeof(*dst), and @usize should've been passed by user space.
> > > > + * The recommended usage is something like the following:
> > > > + *
> > > > + * SYSCALL_DEFINE2(foobar, struct foo __user *, uarg, size_t, usize)
> > > > + * {
> > > > + * int err;
> > > > + * struct foo karg = {};
> > > > + *
> > > > + * // do something with karg
> > > > + *
> > > > + * err = copy_struct_to_user(uarg, usize, &karg, sizeof(karg));
> > > > + * if (err)
> > > > + * return err;
> > > > + *
> > > > + * // ...
> > > > + * }
> > > > + *
> > > > + * There are three cases to consider:
> > > > + * * If @usize == @ksize, then it's copied verbatim.
> > > > + * * If @usize < @ksize, then kernel space is "returning" a newer struct to an
> > > > + * older user space. In order to avoid user space getting incomplete
> > > > + * information (new fields might be important), all trailing bytes in @src
> > > > + * (@ksize - @usize) must be zerored
> > >
> > > s/zerored/zero/, right?
> >
> > It should've been "zeroed".
>
> That reads wrong to me; that way it reads like this function must take
> that action and zero out the 'rest'; which is just wrong.
>
> This function must verify those bytes are zero, not make them zero.
>
> > > > , otherwise -EFBIG is returned.
> > >
> > > 'Funny' that, copy_struct_from_user() below seems to use E2BIG.
> >
> > This is a copy of the semantics that sched_[sg]etattr(2) uses -- E2BIG for
> > a "too big" struct passed to the kernel, and EFBIG for a "too big"
> > struct passed to user-space. I would personally have preferred EMSGSIZE
> > instead of EFBIG, but felt using the existing error codes would be less
> > confusing.
>
> Sadly a recent commit:
>
> 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and robustify sched_read_attr() ABI logic and code")
>
> Made the situation even 'worse'.
And thinking more about things; I'm not convinced the above patch is
actually right.
Do we really want to simply truncate all the attributes of the task?
And should we not at least set sched_flags when there are non-default
clamp values applied?
See; that is I think the primary bug that had chrt failing; we tried to
publish the default clamp values as !0.
next prev parent reply other threads:[~2019-09-05 10:58 UTC|newest]
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 ` Linus Torvalds
2019-09-04 21:00 ` 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 [this message]
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 ` Andreas Schwab
2019-09-05 10:13 ` [PATCH v12 01/12] lib: introduce copy_struct_{to, from}_user helpers 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
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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