linux-stable.git/kernel/events/core.c, branch v4.1.26

ptrace: use fsuid, fsgid, effective creds for fs access checks

2016-04-12T02:07:35+00:00

[ Upstream commit caaee6234d05a58c5b4d05e7bf766131b810a657 ]

By checking the effective credentials instead of the real UID / permitted
capabilities, ensure that the calling process actually intended to use its
credentials.

To ensure that all ptrace checks use the correct caller credentials (e.g.
in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS
flag), use two new flags and require one of them to be set.

The problem was that when a privileged task had temporarily dropped its
privileges, e.g.  by calling setreuid(0, user_uid), with the intent to
perform following syscalls with the credentials of a user, it still passed
ptrace access checks that the user would not be able to pass.

While an attacker should not be able to convince the privileged task to
perform a ptrace() syscall, this is a problem because the ptrace access
check is reused for things in procfs.

In particular, the following somewhat interesting procfs entries only rely
on ptrace access checks:

 /proc/$pid/stat - uses the check for determining whether pointers
     should be visible, useful for bypassing ASLR
 /proc/$pid/maps - also useful for bypassing ASLR
 /proc/$pid/cwd - useful for gaining access to restricted
     directories that contain files with lax permissions, e.g. in
     this scenario:
     lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar
     drwx------ root root /root
     drwxr-xr-x root root /root/foobar
     -rw-r--r-- root root /root/foobar/secret

Therefore, on a system where a root-owned mode 6755 binary changes its
effective credentials as described and then dumps a user-specified file,
this could be used by an attacker to reveal the memory layout of root's
processes or reveal the contents of files he is not allowed to access
(through /proc/$pid/cwd).

[akpm@linux-foundation.org: fix warning]
Signed-off-by: Jann Horn 
Acked-by: Kees Cook 
Cc: Casey Schaufler 
Cc: Oleg Nesterov 
Cc: Ingo Molnar 
Cc: James Morris 
Cc: "Serge E. Hallyn" 
Cc: Andy Shevchenko 
Cc: Andy Lutomirski 
Cc: Al Viro 
Cc: "Eric W. Biederman" 
Cc: Willy Tarreau 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 

Signed-off-by: Sasha Levin

perf/core: Fix perf_sched_count derailment

2016-03-24T12:40:21+00:00

[ Upstream commit 927a5570855836e5d5859a80ce7e91e963545e8f ]

The error path in perf_event_open() is such that asking for a sampling
event on a PMU that doesn't generate interrupts will end up in dropping
the perf_sched_count even though it hasn't been incremented for this
event yet.

Given a sufficient amount of these calls, we'll end up disabling
scheduler's jump label even though we'd still have active events in the
system, thereby facilitating the arrival of the infernal regions upon us.

I'm fixing this by moving account_event() inside perf_event_alloc().

Signed-off-by: Alexander Shishkin 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: 
Cc: Arnaldo Carvalho de Melo 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Cc: Vince Weaver 
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/1456917854-29427-1-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar 
Signed-off-by: He Kuang 
Signed-off-by: Sasha Levin

perf: Cure event->pending_disable race

2016-03-24T12:40:21+00:00

[ Upstream commit 28a967c3a2f99fa3b5f762f25cb2a319d933571b ]

Because event_sched_out() checks event->pending_disable _before_
actually disabling the event, it can happen that the event fires after
it checks but before it gets disabled.

This would leave event->pending_disable set and the queued irq_work
will try and process it.

However, if the event trigger was during schedule(), the event might
have been de-scheduled by the time the irq_work runs, and
perf_event_disable_local() will fail.

Fix this by checking event->pending_disable _after_ we call
event->pmu->del(). This depends on the latter being a compiler
barrier, such that the compiler does not lift the load and re-creates
the problem.

Tested-by: Alexander Shishkin 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174948.040469884@infradead.org
Signed-off-by: Ingo Molnar 
Signed-off-by: He Kuang 
Signed-off-by: Sasha Levin

perf: Do not double free

2016-03-24T12:40:21+00:00

[ Upstream commit 130056275ade730e7a79c110212c8815202773ee ]

In case of: err_file: fput(event_file), we'll end up calling
perf_release() which in turn will free the event.

Do not then free the event _again_.

Tested-by: Alexander Shishkin 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alexander Shishkin 
Cc: Arnaldo Carvalho de Melo 
Cc: Jiri Olsa 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: dvyukov@google.com
Cc: eranian@google.com
Cc: oleg@redhat.com
Cc: panand@redhat.com
Cc: sasha.levin@oracle.com
Cc: vince@deater.net
Link: http://lkml.kernel.org/r/20160224174947.697350349@infradead.org
Signed-off-by: Ingo Molnar 
Signed-off-by: He Kuang 
Signed-off-by: Sasha Levin

perf: Fix AUX buffer refcounting

2015-10-22T21:43:12+00:00

commit 57ffc5ca679f499f4704fd9b6a372916f59930ee upstream.

Its currently possible to drop the last refcount to the aux buffer
from NMI context, which results in the expected fireworks.

The refcounting needs a bigger overhaul, but to cure the immediate
problem, delay the freeing by using an irq_work.

Reviewed-and-tested-by: Alexander Shishkin 
Reported-by: Vince Weaver 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Arnaldo Carvalho de Melo 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20150618103249.GK19282@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

perf: Fix PERF_EVENT_IOC_PERIOD migration race

2015-09-13T16:07:39+00:00

commit c7999c6f3fed9e383d3131474588f282ae6d56b9 upstream.

I ran the perf fuzzer, which triggered some WARN()s which are due to
trying to stop/restart an event on the wrong CPU.

Use the normal IPI pattern to ensure we run the code on the correct CPU.

Signed-off-by: Peter Zijlstra (Intel) 
Cc: Vince Weaver 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: bad7192b842c ("perf: Fix PERF_EVENT_IOC_PERIOD to force-reset the period")
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

perf: Fix running time accounting

2015-09-13T16:07:39+00:00

commit 00a2916f7f82c348a2a94dbb572874173bc308a3 upstream.

A recent fix to the shadow timestamp inadvertly broke the running time
accounting.

We must not update the running timestamp if we fail to schedule the
event, the event will not have ran. This can (and did) result in
negative total runtime because the stopped timestamp was before the
running timestamp (we 'started' but never stopped the event -- because
it never really started we didn't have to stop it either).

Reported-and-Tested-by: Vince Weaver 
Fixes: 72f669c0086f ("perf: Update shadow timestamp before add event")
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Shaohua Li 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

perf: Fix fasync handling on inherited events

2015-09-13T16:07:39+00:00

commit fed66e2cdd4f127a43fd11b8d92a99bdd429528c upstream.

Vince reported that the fasync signal stuff doesn't work proper for
inherited events. So fix that.

Installing fasync allocates memory and sets filp->f_flags |= FASYNC,
which upon the demise of the file descriptor ensures the allocation is
freed and state is updated.

Now for perf, we can have the events stick around for a while after the
original FD is dead because of references from child events. So we
cannot copy the fasync pointer around. We can however consistently use
the parent's fasync, as that will be updated.

Reported-and-Tested-by: Vince Weaver 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Arnaldo Carvalho deMelo 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: eranian@google.com
Link: http://lkml.kernel.org/r/1434011521.1495.71.camel@twins
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

perf: Fix ring_buffer_attach() RCU sync, again

2015-06-29T19:35:28+00:00

commit 2f993cf093643b98477c421fa2b9a98dcc940323 upstream.

While looking for other users of get_state/cond_sync. I Found
ring_buffer_attach() and it looks obviously buggy?

Don't we need to ensure that we have "synchronize" _between_
list_del() and list_add() ?

IOW. Suppose that ring_buffer_attach() preempts right_after
get_state_synchronize_rcu() and gp completes before spin_lock().

In this case cond_synchronize_rcu() does nothing and we reuse
->rb_entry without waiting for gp in between?

It also moves the ->rcu_pending check under "if (rb)", to make it
more readable imo.

Signed-off-by: Oleg Nesterov 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Alexander Shishkin 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: dave@stgolabs.net
Cc: der.herr@hofr.at
Cc: josh@joshtriplett.org
Cc: tj@kernel.org
Fixes: b69cf53640da ("perf: Fix a race between ring_buffer_detach() and ring_buffer_attach()")
Link: http://lkml.kernel.org/r/20150530200425.GA15748@redhat.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

perf: Fix race in BPF program unregister

2015-05-27T06:46:15+00:00

there is a race between perf_event_free_bpf_prog() and free_trace_kprobe():

	__free_event()
	  event->destroy(event)
	    tp_perf_event_destroy()
	      perf_trace_destroy()
		perf_trace_event_unreg()

which is dropping event->tp_event->perf_refcount and allows to proceed in:

	unregister_trace_kprobe()
	  unregister_kprobe_event()
	      trace_remove_event_call()
		    probe_remove_event_call()
	free_trace_kprobe()

while __free_event does:

	call_rcu(&event->rcu_head, free_event_rcu);
	  free_event_rcu()
	    perf_event_free_bpf_prog()

To fix the race simply move perf_event_free_bpf_prog() before
event->destroy(), since event->tp_event is still valid at that point.

Note, perf_trace_destroy() is not racing with trace_remove_event_call()
since they both grab event_mutex.

Reported-by: Wang Nan 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: Arnaldo Carvalho de Melo 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: lizefan@huawei.com
Cc: pi3orama@163.com
Fixes: 2541517c32be ("tracing, perf: Implement BPF programs attached to kprobes")
Link: http://lkml.kernel.org/r/1431717321-28772-1-git-send-email-ast@plumgrid.com
Signed-off-by: Ingo Molnar