LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Howells <dhowells@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access()
Date: Wed, 29 May 2019 11:55:44 -0700	[thread overview]
Message-ID: <201905291154.E4A0CB717@keescook> (raw)
In-Reply-To: <20190529113157.227380-1-jannh@google.com>

On Wed, May 29, 2019 at 01:31:57PM +0200, Jann Horn wrote:
> Restore the read memory barrier in __ptrace_may_access() that was deleted
> a couple years ago. Also add comments on this barrier and the one it pairs
> with to explain why they're there (as far as I understand).
> 
> Fixes: bfedb589252c ("mm: Add a user_ns owner to mm_struct and fix ptrace permission checks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Jann Horn <jannh@google.com>

Ah, thanks! Nice find.

Acked-by: Kees Cook <keescook@chromium.org>

(And, yeah, Eric, I say snag it if you've got stuff queued up...)

-Kees

> ---
> (I have no clue whatsoever what the relevant tree for this is, but I
> guess Oleg is the relevant maintainer?)
> 
>  kernel/cred.c   |  9 +++++++++
>  kernel/ptrace.c | 10 ++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/kernel/cred.c b/kernel/cred.c
> index 45d77284aed0..07e069d00696 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -450,6 +450,15 @@ int commit_creds(struct cred *new)
>  		if (task->mm)
>  			set_dumpable(task->mm, suid_dumpable);
>  		task->pdeath_signal = 0;
> +		/*
> +		 * If a task drops privileges and becomes nondumpable,
> +		 * the dumpability change must become visible before
> +		 * the credential change; otherwise, a __ptrace_may_access()
> +		 * racing with this change may be able to attach to a task it
> +		 * shouldn't be able to attach to (as if the task had dropped
> +		 * privileges without becoming nondumpable).
> +		 * Pairs with a read barrier in __ptrace_may_access().
> +		 */
>  		smp_wmb();
>  	}
>  
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 5710d07e67cf..e54452c2954b 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -324,6 +324,16 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
>  	return -EPERM;
>  ok:
>  	rcu_read_unlock();
> +	/*
> +	 * If a task drops privileges and becomes nondumpable (through a syscall
> +	 * like setresuid()) while we are trying to access it, we must ensure
> +	 * that the dumpability is read after the credentials; otherwise,
> +	 * we may be able to attach to a task that we shouldn't be able to
> +	 * attach to (as if the task had dropped privileges without becoming
> +	 * nondumpable).
> +	 * Pairs with a write barrier in commit_creds().
> +	 */
> +	smp_rmb();
>  	mm = task->mm;
>  	if (mm &&
>  	    ((get_dumpable(mm) != SUID_DUMP_USER) &&
> -- 
> 2.22.0.rc1.257.g3120a18244-goog
> 

-- 
Kees Cook

  parent reply	other threads:[~2019-05-29 18:55 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 11:31 Jann Horn
2019-05-29 15:59 ` Eric W. Biederman
2019-05-29 16:01   ` Jann Horn
2019-05-29 16:21 ` Oleg Nesterov
2019-05-29 17:38   ` Jann Horn
2019-05-30  1:41     ` Eric W. Biederman
2019-05-31 15:04       ` Jann Horn
2019-05-30 10:34     ` Andrea Parri
2019-05-31  9:08       ` Peter Zijlstra
2019-05-30 12:05     ` Oleg Nesterov
2019-05-31  9:12       ` Peter Zijlstra
2019-05-31  9:55         ` Oleg Nesterov
2019-05-29 21:02   ` Jann Horn
2019-05-29 18:55 ` Kees Cook [this message]
2019-05-30 12:34 ` Oleg Nesterov
2019-05-31 11:56   ` Jann Horn
2019-05-31 13:35     ` Oleg Nesterov
2019-05-31 19:37       ` Jann Horn

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=201905291154.E4A0CB717@keescook \
    --to=keescook@chromium.org \
    --cc=akpm@linux-foundation.org \
    --cc=dhowells@redhat.com \
    --cc=ebiederm@xmission.com \
    --cc=jannh@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=oleg@redhat.com \
    --subject='Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access()' \
    /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

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).