Date:   Mon,  9 Apr 2018 19:03:46 +0900
From:   Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] perf/core: fix use-after-free in uprobe_perf_close

A use-after-free bug was caught by KASAN while running usdt related
code. (BCC project. bcc/tests/python/test_usdt2.py)

==================================================================
BUG: KASAN: use-after-free in uprobe_perf_close+0x222/0x3b0
Read of size 4 at addr ffff880384f9b4a4 by task test_usdt2.py/870

CPU: 4 PID: 870 Comm: test_usdt2.py Tainted: G        W         4.16.0-next-20180409 #215
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
Call Trace:
 dump_stack+0xc7/0x15b
 ? show_regs_print_info+0x5/0x5
 ? printk+0x9c/0xc3
 ? kmsg_dump_rewind_nolock+0x6e/0x6e
 ? uprobe_perf_close+0x222/0x3b0
 print_address_description+0x83/0x3a0
 ? uprobe_perf_close+0x222/0x3b0
 kasan_report+0x1dd/0x460
 ? uprobe_perf_close+0x222/0x3b0
 uprobe_perf_close+0x222/0x3b0
 ? probes_open+0x180/0x180
 ? free_filters_list+0x290/0x290
 trace_uprobe_register+0x1bb/0x500
 ? perf_event_attach_bpf_prog+0x310/0x310
 ? probe_event_disable+0x4e0/0x4e0
 perf_uprobe_destroy+0x63/0xd0
 _free_event+0x2bc/0xbd0
 ? lockdep_rcu_suspicious+0x100/0x100
 ? ring_buffer_attach+0x550/0x550
 ? kvm_sched_clock_read+0x1a/0x30
 ? perf_event_release_kernel+0x3e4/0xc00
 ? __mutex_unlock_slowpath+0x12e/0x540
 ? wait_for_completion+0x430/0x430
 ? lock_downgrade+0x3c0/0x3c0
 ? lock_release+0x980/0x980
 ? do_raw_spin_trylock+0x118/0x150
 ? do_raw_spin_unlock+0x121/0x210
 ? do_raw_spin_trylock+0x150/0x150
 perf_event_release_kernel+0x5d4/0xc00
 ? put_event+0x30/0x30
 ? fsnotify+0xd2d/0xea0
 ? sched_clock_cpu+0x18/0x1a0
 ? __fsnotify_update_child_dentry_flags.part.0+0x1b0/0x1b0
 ? pvclock_clocksource_read+0x152/0x2b0
 ? pvclock_read_flags+0x80/0x80
 ? kvm_sched_clock_read+0x1a/0x30
 ? sched_clock_cpu+0x18/0x1a0
 ? pvclock_clocksource_read+0x152/0x2b0
 ? locks_remove_file+0xec/0x470
 ? pvclock_read_flags+0x80/0x80
 ? fcntl_setlk+0x880/0x880
 ? ima_file_free+0x8d/0x390
 ? lockdep_rcu_suspicious+0x100/0x100
 ? ima_file_check+0x110/0x110
 ? fsnotify+0xea0/0xea0
 ? kvm_sched_clock_read+0x1a/0x30
 ? rcu_note_context_switch+0x600/0x600
 perf_release+0x21/0x40
 __fput+0x264/0x620
 ? fput+0xf0/0xf0
 ? do_raw_spin_unlock+0x121/0x210
 ? do_raw_spin_trylock+0x150/0x150
 ? SyS_fchdir+0x100/0x100
 ? fsnotify+0xea0/0xea0
 task_work_run+0x14b/0x1e0
 ? task_work_cancel+0x1c0/0x1c0
 ? copy_fd_bitmaps+0x150/0x150
 ? vfs_read+0xe5/0x260
 exit_to_usermode_loop+0x17b/0x1b0
 ? trace_event_raw_event_sys_exit+0x1a0/0x1a0
 do_syscall_64+0x3f6/0x490
 ? syscall_return_slowpath+0x2c0/0x2c0
 ? lockdep_sys_exit+0x1f/0xaa
 ? syscall_return_slowpath+0x1a3/0x2c0
 ? lockdep_sys_exit+0x1f/0xaa
 ? prepare_exit_to_usermode+0x11c/0x1e0
 ? enter_from_user_mode+0x30/0x30
random: crng init done
 ? __put_user_4+0x1c/0x30
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x7f41d95f9340
RSP: 002b:00007fffe71e4268 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 000000000000000d RCX: 00007f41d95f9340
RDX: 0000000000000000 RSI: 0000000000002401 RDI: 000000000000000d
RBP: 0000000000000000 R08: 00007f41ca8ff700 R09: 00007f41d996dd1f
R10: 00007fffe71e41e0 R11: 0000000000000246 R12: 00007fffe71e4330
R13: 0000000000000000 R14: fffffffffffffffc R15: 00007fffe71e4290

Allocated by task 870:
 kasan_kmalloc+0xa0/0xd0
 kmem_cache_alloc_node+0x11a/0x430
 copy_process.part.19+0x11a0/0x41c0
 _do_fork+0x1be/0xa20
 do_syscall_64+0x198/0x490
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2

Freed by task 0:
 __kasan_slab_free+0x12e/0x180
 kmem_cache_free+0x102/0x4d0
 free_task+0xfe/0x160
 __put_task_struct+0x189/0x290
 delayed_put_task_struct+0x119/0x250
 rcu_process_callbacks+0xa6c/0x1b60
 __do_softirq+0x238/0x7ae

The buggy address belongs to the object at ffff880384f9b480
 which belongs to the cache task_struct of size 12928

It occurs because task_struct is freed before perf_event which refers
to the task and task flags are checked while teardown of the event.
perf_event_alloc() assigns task_struct to hw.target of perf_event,
but there is no reference counting for it.

As a fix we get_task_struct() in perf_event_alloc() at above mentioned
assignment and put_task_struct() in _free_event().

Signed-off-by: Prashant Bhole <bhole_prashant_q7@....ntt.co.jp>
---
 kernel/events/core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1922f2e0980a..734192a718ec 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4447,6 +4447,9 @@ static void _free_event(struct perf_event *event)
 	if (event->ctx)
 		put_ctx(event->ctx);
 
+	if (event->hw.target)
+		put_task_struct(event->hw.target);
+
 	exclusive_event_destroy(event);
 	module_put(event->pmu->module);
 
@@ -9955,6 +9958,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 		 * and we cannot use the ctx information because we need the
 		 * pmu before we get a ctx.
 		 */
+		get_task_struct(task);
 		event->hw.target = task;
 	}
 
@@ -10070,6 +10074,8 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 		perf_detach_cgroup(event);
 	if (event->ns)
 		put_pid_ns(event->ns);
+	if (event->hw.target)
+		put_task_struct(event->hw.target);
 	kfree(event);
 
 	return ERR_PTR(err);
-- 
2.13.6

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