[PATCH] perf/core: fix use-after-free in uprobe_perf_close
From: Prashant Bhole
Date: Mon Apr 09 2018 - 06:25:25 EST
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@xxxxxxxxxxxxx>
---
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