From: Marco Elver <elver@google.com>
To: elver@google.com, peterz@infradead.org
Cc: tglx@linutronix.de, mingo@kernel.org, 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,
Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH v2] perf: Require CAP_KILL if sigtrap is requested
Date: Thu, 1 Jul 2021 10:38:43 +0200 [thread overview]
Message-ID: <20210701083842.580466-1-elver@google.com> (raw)
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.
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>
---
v2:
* 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).
---
kernel/events/core.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index fe88d6eea3c2..43c99695dc3f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12152,10 +12152,23 @@ SYSCALL_DEFINE5(perf_event_open,
}
if (task) {
+ 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 have CAP_KILL.
+ */
+ rcu_read_lock();
+ is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL);
+ rcu_read_unlock();
+ }
+
/*
* Preserve ptrace permission check for backwards compatibility.
*
@@ -12165,7 +12178,7 @@ 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_READ_REALCREDS))
goto err_cred;
}
--
2.32.0.93.g670b81a890-goog
next reply other threads:[~2021-07-01 8:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-01 8:38 Marco Elver [this message]
2021-07-01 21:41 ` [PATCH v2] perf: Require CAP_KILL if sigtrap is requested Eric W. Biederman
2021-07-02 7:20 ` Marco Elver
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