linux-kernel - Re: [PATCH v2 0/3] bpf: switch to new usercopy helpers

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Message-ID: <20191016004809.tgw6zznr6ukppplp@wittgenstein>
Date:   Wed, 16 Oct 2019 02:48:10 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     ast@...nel.org
Cc:     bpf@...r.kernel.org, daniel@...earbox.net, kafai@...com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        songliubraving@...com, yhs@...com
Subject: Re: [PATCH v2 0/3] bpf: switch to new usercopy helpers

On Wed, Oct 16, 2019 at 02:41:35AM +0200, Christian Brauner wrote:
> Hey everyone,
> 
> In v5.4-rc2 we added two new helpers check_zeroed_user() and
> copy_struct_from_user() including selftests (cf. [1]). It is a generic
> interface designed to copy a struct from userspace. The helpers will be
> especially useful for structs versioned by size of which we have quite a
> few.
> 
> The most obvious benefit is that this helper lets us get rid of
> duplicate code. We've already switched over sched_setattr(), perf_event_open(),
> and clone3(). More importantly it will also help to ensure that users
> implementing versioning-by-size end up with the same core semantics.
> 
> This point is especially crucial since we have at least one case where
> versioning-by-size is used but with slighly different semantics:
> sched_setattr(), perf_event_open(), and clone3() all do do similar
> checks to copy_struct_from_user() while rt_sigprocmask(2) always rejects
> differently-sized struct arguments.
> 
> This little series switches over bpf codepaths that have hand-rolled
> implementations of these helpers.
> 
> Thanks!
> Christian
> 
> /* v1 */
> Link: https://lore.kernel.org/r/20191009160907.10981-1-christian.brauner@ubuntu.com
> 
> /* v2 */
> - rebase onto bpf-next
> 
> /* Reference */
> [1]: f5a1a536fa14 ("lib: introduce copy_struct_from_user() helper")

Alexei, instead of applying the series you can also just pull from me:

The following changes since commit 5bc60de50dfea235634fdf38cbc992fb968d113b:

  selftests: bpf: Don't try to read files without read permission (2019-10-15 16:27:25 -0700)

are available in the Git repository at:

  git@...olite.kernel.org:pub/scm/linux/kernel/git/brauner/linux tags/bpf-copy-struct-from-user

for you to fetch changes up to da1699b959d182bb161be3ffc17eab063b2aedd2:

  bpf: use copy_struct_from_user() in bpf() syscall (2019-10-16 02:35:11 +0200)

----------------------------------------------------------------
bpf-copy-struct-from-user

----------------------------------------------------------------
Christian Brauner (3):
      bpf: use check_zeroed_user() in bpf_check_uarg_tail_zero()
      bpf: use copy_struct_from_user() in bpf_prog_get_info_by_fd()
      bpf: use copy_struct_from_user() in bpf() syscall

 kernel/bpf/syscall.c | 46 ++++++++++++++++++----------------------------
 1 file changed, 18 insertions(+), 28 deletions(-)