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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Qian Cai <cai@lca.pw>
Cc:     tglx@linutronix.de, oleg@redhat.com, linux-kernel@vger.kernel.org
References: <20200304004336.960-1-cai@lca.pw>
Date:   Tue, 03 Mar 2020 23:15:43 -0600
In-Reply-To: <20200304004336.960-1-cai@lca.pw> (Qian Cai's message of "Tue, 3
        Mar 2020 19:43:36 -0500")
Message-ID: <87eeu8hf9c.fsf@x220.int.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [PATCH -next] posix-cpu-timers: fix memory leaks for task_struct
Sender: linux-kernel-owner@vger.kernel.org
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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;
>  }