From: Marco Elver <elver@google.com>
To: elver@google.com, peterz@infradead.org
Cc: tglx@linutronix.de, mingo@kernel.org, dvyukov@google.com,
glider@google.com, kasan-dev@googlegroups.com,
linux-kernel@vger.kernel.org, mingo@redhat.com, acme@kernel.org,
mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
jolsa@redhat.com, namhyung@kernel.org,
linux-perf-users@vger.kernel.org, ebiederm@xmission.com,
omosnace@redhat.com, serge@hallyn.com,
linux-security-module@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v3 1/2] perf: Fix required permissions if sigtrap is requested
Date: Mon, 12 Jul 2021 12:32:33 +0200 [thread overview]
Message-ID: <CANpmjNP7Z0mxaF+eYCtP1aabPcoh-0aDSOiW6FQsPkR8SbVwnA@mail.gmail.com> (raw)
In-Reply-To: <20210705084453.2151729-1-elver@google.com>
It'd be good to get this sorted -- please take another look.
Many thanks,
-- Marco
On Mon, 5 Jul 2021 at 10:45, Marco Elver <elver@google.com> wrote:
> If perf_event_open() is called with another task as target and
> perf_event_attr::sigtrap is set, and the target task's user does not
> match the calling user, also require the CAP_KILL capability or
> PTRACE_MODE_ATTACH permissions.
>
> Otherwise, with the CAP_PERFMON capability alone it would be possible
> for a user to send SIGTRAP signals via perf events to another user's
> tasks. This could potentially result in those tasks being terminated if
> they cannot handle SIGTRAP signals.
>
> Note: The check complements the existing capability check, but is not
> supposed to supersede the ptrace_may_access() check. At a high level we
> now have:
>
> capable of CAP_PERFMON and (CAP_KILL if sigtrap)
> OR
> ptrace_may_access(...) // also checks for same thread-group and uid
>
> Fixes: 97ba62b27867 ("perf: Add support for SIGTRAP on perf events")
> Cc: <stable@vger.kernel.org> # 5.13+
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> v3:
> * Upgrade ptrace mode check to ATTACH if attr.sigtrap, otherwise it's
> possible to change the target task (send signal) even if only read
> ptrace permissions were granted (reported by Eric W. Biederman).
>
> v2: https://lkml.kernel.org/r/20210701083842.580466-1-elver@google.com
> * Drop kill_capable() and just check CAP_KILL (reported by Ondrej Mosnacek).
> * Use ns_capable(__task_cred(task)->user_ns, CAP_KILL) to check for
> capability in target task's ns (reported by Ondrej Mosnacek).
>
> v1: https://lkml.kernel.org/r/20210630093709.3612997-1-elver@google.com
> ---
> kernel/events/core.c | 25 ++++++++++++++++++++++++-
> 1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index fe88d6eea3c2..f79ee82e644a 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -12152,10 +12152,33 @@ SYSCALL_DEFINE5(perf_event_open,
> }
>
> if (task) {
> + unsigned int ptrace_mode = PTRACE_MODE_READ_REALCREDS;
> + bool is_capable;
> +
> err = down_read_interruptible(&task->signal->exec_update_lock);
> if (err)
> goto err_file;
>
> + is_capable = perfmon_capable();
> + if (attr.sigtrap) {
> + /*
> + * perf_event_attr::sigtrap sends signals to the other
> + * task. Require the current task to also have
> + * CAP_KILL.
> + */
> + rcu_read_lock();
> + is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL);
> + rcu_read_unlock();
> +
> + /*
> + * If the required capabilities aren't available, checks
> + * for ptrace permissions: upgrade to ATTACH, since
> + * sending signals can effectively change the target
> + * task.
> + */
> + ptrace_mode = PTRACE_MODE_ATTACH_REALCREDS;
> + }
> +
> /*
> * Preserve ptrace permission check for backwards compatibility.
> *
> @@ -12165,7 +12188,7 @@ SYSCALL_DEFINE5(perf_event_open,
> * perf_event_exit_task() that could imply).
> */
> err = -EACCES;
> - if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
> + if (!is_capable && !ptrace_may_access(task, ptrace_mode))
> goto err_cred;
> }
>
> --
> 2.32.0.93.g670b81a890-goog
>
next prev parent reply other threads:[~2021-07-12 10:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-05 8:44 [PATCH v3 1/2] perf: Fix required permissions if sigtrap is requested Marco Elver
2021-07-05 8:44 ` [PATCH v3 2/2] perf: Refactor permissions check into perf_check_permission() Marco Elver
2021-07-06 6:16 ` Dmitry Vyukov
2021-07-27 13:58 ` [tip: perf/urgent] " tip-bot2 for Marco Elver
2021-07-06 6:16 ` [PATCH v3 1/2] perf: Fix required permissions if sigtrap is requested Dmitry Vyukov
2021-07-12 10:32 ` Marco Elver [this message]
2021-07-13 9:48 ` Peter Zijlstra
2021-07-27 13:58 ` [tip: perf/urgent] " tip-bot2 for Marco Elver
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=CANpmjNP7Z0mxaF+eYCtP1aabPcoh-0aDSOiW6FQsPkR8SbVwnA@mail.gmail.com \
--to=elver@google.com \
--cc=acme@kernel.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=dvyukov@google.com \
--cc=ebiederm@xmission.com \
--cc=glider@google.com \
--cc=jolsa@redhat.com \
--cc=kasan-dev@googlegroups.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@kernel.org \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=omosnace@redhat.com \
--cc=peterz@infradead.org \
--cc=serge@hallyn.com \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
/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).