From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>,
Kees Cook <keescook@chromium.org>
Subject: [patch 5/6] posix-cpu-timers: Sanitize thread clock permissions
Date: Thu, 05 Sep 2019 14:03:44 +0200 [thread overview]
Message-ID: <20190905120540.068959005@linutronix.de> (raw)
In-Reply-To: 20190905120339.561100423@linutronix.de
The thread clock permissions are restricted to tasks of the same thread
group, but that also prevents a ptracer from reading them. This is
inconsistent vs. the process restrictions and unnecessary strict.
Relax it to ptrace permissions in the same way as process permissions are
handled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/posix-cpu-timers.c | 56 +++++++++++++++++++++--------------------
1 file changed, 29 insertions(+), 27 deletions(-)
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -51,6 +51,7 @@ void update_rlimit_cpu(struct task_struc
static struct task_struct *lookup_task(const pid_t pid, bool thread,
bool gettime)
{
+ unsigned int mode = PTRACE_MODE_ATTACH_REALCREDS;
struct task_struct *p;
/*
@@ -64,44 +65,45 @@ static struct task_struct *lookup_task(c
if (!p)
return p;
- if (thread)
- return same_thread_group(p, current) ? p : NULL;
-
if (gettime) {
/*
* For clock_gettime() the task does not need to be the
* actual group leader. tsk->sighand gives access to the
- * group's clock. current can obviously access itself, so
- * spare the ptrace check below.
+ * group's clock.
+ *
+ * The trivial case is that p is current or in the same
+ * thread group, i.e. sharing p->signal. Spare the ptrace
+ * check in that case.
*/
- if (p == current)
+ if (same_thread_group(p, current))
return p;
- if (!thread_group_leader(p))
- return NULL;
+ mode = PTRACE_MODE_READ_REALCREDS;
- if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
- return NULL;
- return p;
- }
+ } else if (thread) {
+ /*
+ * Timer is going to be attached to a thread. If p is
+ * current or in the same thread group, granted.
+ */
+ if (same_thread_group(p, current))
+ return p;
- /*
- * For processes require that p is group leader.
- */
- if (!has_group_leader_pid(p))
- return NULL;
+ } else {
+ /*
+ * For processes require that p is group leader.
+ */
+ if (!has_group_leader_pid(p))
+ return NULL;
- /*
- * Avoid the ptrace overhead when this is current's process
- */
- if (same_thread_group(p, current))
- return p;
+ /*
+ * Avoid the ptrace overhead when this is current's process
+ */
+ if (same_thread_group(p, current))
+ return p;
+ }
- /*
- * Creating timers on processes which cannot be ptraced is not
- * permitted:
- */
- return ptrace_may_access(p, PTRACE_MODE_ATTACH_REALCREDS) ? p : NULL;
+ /* Decide based on the ptrace permissions. */
+ return ptrace_may_access(p, mode) ? p : NULL;
}
static struct task_struct *__get_task_for_clock(const clockid_t clock,
next prev parent reply other threads:[~2019-09-05 12:12 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-05 12:03 [patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening Thomas Gleixner
2019-09-05 12:03 ` [patch 1/6] posix-cpu-timers: Always clear head pointer on dequeue Thomas Gleixner
2019-09-05 15:49 ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 2/6] posix-cpu-timers: Fix permission check regression Thomas Gleixner
2019-09-05 17:31 ` Frederic Weisbecker
2019-09-05 18:55 ` Thomas Gleixner
2019-09-05 21:15 ` [patch V2 " Thomas Gleixner
2019-09-09 15:13 ` Frederic Weisbecker
2019-09-10 11:18 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2019-09-05 12:03 ` [patch 3/6] posix-cpu-timers: Restrict timer_create() permissions Thomas Gleixner
2019-09-21 0:44 ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 4/6] posix-cpu-timers: Restrict clock_gettime() permissions Thomas Gleixner
2019-09-23 13:39 ` Frederic Weisbecker
2019-09-05 12:03 ` Thomas Gleixner [this message]
2019-09-05 12:21 ` [patch 5/6] posix-cpu-timers: Sanitize thread clock permissions Peter Zijlstra
2019-09-05 14:11 ` Thomas Gleixner
2019-09-23 14:03 ` Frederic Weisbecker
2019-09-05 12:03 ` [patch 6/6] posix-cpu-timers: Make PID=0 and PID=self handling consistent Thomas Gleixner
2019-09-23 14:13 ` Frederic Weisbecker
2019-09-23 14:17 ` Thomas Gleixner
2019-09-05 14:48 ` [patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening Frederic Weisbecker
2019-09-05 14:57 ` Thomas Gleixner
2019-09-05 15:21 ` Frederic Weisbecker
2019-09-05 20:32 ` Kees Cook
2019-09-05 21:13 ` Thomas Gleixner
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