[PATCH -next] posix-cpu-timers: fix memory leaks for task_struct

[PATCH -next] posix-cpu-timers: fix memory leaks for task_struct

[Qian Cai]

The recent commit removed put_task_struct() in posix_cpu_timer_del()
results in many memory leaks like this,

unreferenced object 0xc0000016d9b44480 (size 8192):
  comm "timer_create01", pid 57749, jiffies 4295163733 (age 6159.670s)
  hex dump (first 32 bytes):
    02 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<0000000056aca129>] copy_process+0x26c/0x18e0
    alloc_task_struct_node at kernel/fork.c:169
    (inlined by) dup_task_struct at kernel/fork.c:877
    (inlined by) copy_process at kernel/fork.c:1929
    [<00000000bdbbf9f8>] _do_fork+0xac/0xb20
    [<00000000dcb1c445>] __do_sys_clone+0x98/0xe0
    __do_sys_clone at kernel/fork.c:2591
    [<000000006c059205>] ppc_clone+0x8/0xc
    ppc_clone at arch/powerpc/kernel/entry_64.S:479

Fixes: 672ebe8eb017a5 ("posix-cpu-timers: Store a reference to a pid not a task")
Signed-off-by: Qian Cai <cai@lca.pw>
---
 kernel/time/posix-cpu-timers.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index afd1e959a282..e0b580deb61a 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -446,8 +446,10 @@ static int posix_cpu_timer_del(struct k_itimer *timer)
 
 out:
 	rcu_read_unlock();
-	if (!ret)
+	if (!ret) {
 		put_pid(ctmr->pid);
+		put_task_struct(p);
+	}
 
 	return ret;
 }
-- 
2.21.0 (Apple Git-122.2)

Re: [PATCH -next] posix-cpu-timers: fix memory leaks for task_struct

[Eric W. Biederman]

Qian Cai <cai@lca.pw> writes:

> The recent commit removed put_task_struct() in posix_cpu_timer_del()
> results in many memory leaks like this,

Good spotting but no.  The leak is in posix_cpu_timer_create.
There is a strong likely hood but no guarantee that the task
in posix_cpu_timer_del is the same as the task in
posix_cpu_timer_create.

Plus the point of it all is to use pid references instead of task
references.

Thank you very much for catching my braino.

Eric


> unreferenced object 0xc0000016d9b44480 (size 8192):
>   comm "timer_create01", pid 57749, jiffies 4295163733 (age 6159.670s)
>   hex dump (first 32 bytes):
>     02 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<0000000056aca129>] copy_process+0x26c/0x18e0
>     alloc_task_struct_node at kernel/fork.c:169
>     (inlined by) dup_task_struct at kernel/fork.c:877
>     (inlined by) copy_process at kernel/fork.c:1929
>     [<00000000bdbbf9f8>] _do_fork+0xac/0xb20
>     [<00000000dcb1c445>] __do_sys_clone+0x98/0xe0
>     __do_sys_clone at kernel/fork.c:2591
>     [<000000006c059205>] ppc_clone+0x8/0xc
>     ppc_clone at arch/powerpc/kernel/entry_64.S:479
>
> Fixes: 672ebe8eb017a5 ("posix-cpu-timers: Store a reference to a pid not a task")
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
>  kernel/time/posix-cpu-timers.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
> index afd1e959a282..e0b580deb61a 100644
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -446,8 +446,10 @@ static int posix_cpu_timer_del(struct k_itimer *timer)
>  
>  out:
>  	rcu_read_unlock();
> -	if (!ret)
> +	if (!ret) {
>  		put_pid(ctmr->pid);
> +		put_task_struct(p);
> +	}
>  
>  	return ret;
>  }

[PATCH timers/core] posix-cpu-timers: Put the task_struct in posix_cpu_timers_create

[Eric W. Biederman]

Qian Cai <cai@lca.pw> writes:
> The recent commit removed put_task_struct() in posix_cpu_timer_del()
> results in many memory leaks like this,
>
> unreferenced object 0xc0000016d9b44480 (size 8192):
>   comm "timer_create01", pid 57749, jiffies 4295163733 (age 6159.670s)
>   hex dump (first 32 bytes):
>     02 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<0000000056aca129>] copy_process+0x26c/0x18e0
>     alloc_task_struct_node at kernel/fork.c:169
>     (inlined by) dup_task_struct at kernel/fork.c:877
>     (inlined by) copy_process at kernel/fork.c:1929
>     [<00000000bdbbf9f8>] _do_fork+0xac/0xb20
>     [<00000000dcb1c445>] __do_sys_clone+0x98/0xe0
>     __do_sys_clone at kernel/fork.c:2591
>     [<000000006c059205>] ppc_clone+0x8/0xc
>     ppc_clone at arch/powerpc/kernel/entry_64.S:479
>

I forgot that get_task_for_clock called by posix_cpu_timer_create
returns a reference to a task_struct.  Put that reference
to avoid the leak.

Link: https://lore.kernel.org/lkml/20200304004336.960-1-cai@lca.pw/
Fixes: 672ebe8eb017a5 ("posix-cpu-timers: Store a reference to a pid not a task")
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 kernel/time/posix-cpu-timers.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 1c21f2fd3d9b..cd88c1217224 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -405,6 +405,7 @@ static int posix_cpu_timer_create(struct k_itimer *new_timer)
 	new_timer->kclock = &clock_posix_cpu;
 	timerqueue_init(&new_timer->it.cpu.node);
 	new_timer->it.cpu.pid = get_task_pid(p, cpu_timer_pid_type(new_timer));
+	put_task_struct(p);
 	return 0;
 }
 
-- 
2.20.1

Re: [PATCH timers/core] posix-cpu-timers: Put the task_struct in posix_cpu_timers_create

[Thomas Gleixner]

ebiederm@xmission.com (Eric W. Biederman) writes:

> Qian Cai <cai@lca.pw> writes:
>> The recent commit removed put_task_struct() in posix_cpu_timer_del()
>> results in many memory leaks like this,
>>
>> unreferenced object 0xc0000016d9b44480 (size 8192):
>>   comm "timer_create01", pid 57749, jiffies 4295163733 (age 6159.670s)
>>   hex dump (first 32 bytes):
>>     02 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
>>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>   backtrace:
>>     [<0000000056aca129>] copy_process+0x26c/0x18e0
>>     alloc_task_struct_node at kernel/fork.c:169
>>     (inlined by) dup_task_struct at kernel/fork.c:877
>>     (inlined by) copy_process at kernel/fork.c:1929
>>     [<00000000bdbbf9f8>] _do_fork+0xac/0xb20
>>     [<00000000dcb1c445>] __do_sys_clone+0x98/0xe0
>>     __do_sys_clone at kernel/fork.c:2591
>>     [<000000006c059205>] ppc_clone+0x8/0xc
>>     ppc_clone at arch/powerpc/kernel/entry_64.S:479
>>
>
> I forgot that get_task_for_clock called by posix_cpu_timer_create
> returns a reference to a task_struct.  Put that reference
> to avoid the leak.

I took the liberty to fold this back into the affected commit and add a
comment why this put_task_struct() is actually required.

Thanks,

        tglx

Re: [PATCH timers/core] posix-cpu-timers: Put the task_struct in posix_cpu_timers_create

[Eric W. Biederman]

Thomas Gleixner <tglx@linutronix.de> writes:

> ebiederm@xmission.com (Eric W. Biederman) writes:
>
>> Qian Cai <cai@lca.pw> writes:
>>> The recent commit removed put_task_struct() in posix_cpu_timer_del()
>>> results in many memory leaks like this,
>>>
>>> unreferenced object 0xc0000016d9b44480 (size 8192):
>>>   comm "timer_create01", pid 57749, jiffies 4295163733 (age 6159.670s)
>>>   hex dump (first 32 bytes):
>>>     02 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00  ................
>>>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>>   backtrace:
>>>     [<0000000056aca129>] copy_process+0x26c/0x18e0
>>>     alloc_task_struct_node at kernel/fork.c:169
>>>     (inlined by) dup_task_struct at kernel/fork.c:877
>>>     (inlined by) copy_process at kernel/fork.c:1929
>>>     [<00000000bdbbf9f8>] _do_fork+0xac/0xb20
>>>     [<00000000dcb1c445>] __do_sys_clone+0x98/0xe0
>>>     __do_sys_clone at kernel/fork.c:2591
>>>     [<000000006c059205>] ppc_clone+0x8/0xc
>>>     ppc_clone at arch/powerpc/kernel/entry_64.S:479
>>>
>>
>> I forgot that get_task_for_clock called by posix_cpu_timer_create
>> returns a reference to a task_struct.  Put that reference
>> to avoid the leak.
>
> I took the liberty to fold this back into the affected commit and add a
> comment why this put_task_struct() is actually required.

Good enough.

We should be able to use rcu and remove the reference entirely.
But that is a change for another day.

Eric