From: ebiederm@gmail.com (Eric W. Biederman)
To: madhuparnabhowmik10@gmail.com
Cc: paulmck@kernel.org, linux-kernel@vger.kernel.org,
oleg@redhat.com, joel@joelfernandes.org, ebiederm@xmission.com,
tj@kernel.org, christian.brauner@ubuntu.com,
linux-kernel-mentees@lists.linuxfoundation.org, guro@fb.com
Subject: Re: [Linux-kernel-mentees] [PATCH] signal.c: Fix sparse warnings
Date: Wed, 05 Feb 2020 16:59:52 -0600 [thread overview]
Message-ID: <87wo90myhj.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20200205172437.10113-1-madhuparnabhowmik10@gmail.com> (madhuparnabhowmik's message of "Wed, 5 Feb 2020 22:54:37 +0530")
madhuparnabhowmik10@gmail.com writes:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
>
> This patch fixes the following two sparse warnings caused due to
> accessing RCU protected pointer tsk->parent without rcu primitives.
>
> kernel/signal.c:1948:65: warning: incorrect type in argument 1 (different address spaces)
> kernel/signal.c:1948:65: expected struct task_struct *tsk
> kernel/signal.c:1948:65: got struct task_struct [noderef] <asn:4> *parent
> kernel/signal.c:1949:40: warning: incorrect type in argument 1 (different address spaces)
> kernel/signal.c:1949:40: expected void const volatile *p
> kernel/signal.c:1949:40: got struct cred const [noderef] <asn:4> *[noderef] <asn:4> *
> kernel/signal.c:1949:40: warning: incorrect type in argument 1 (different address spaces)
> kernel/signal.c:1949:40: expected void const volatile *p
> kernel/signal.c:1949:40: got struct cred const [noderef] <asn:4> *[noderef] <asn:4> *
>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> ---
> kernel/signal.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 9ad8dea93dbb..8227058ea8c4 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1945,8 +1945,8 @@ bool do_notify_parent(struct task_struct *tsk, int sig)
> * correct to rely on this
> */
> rcu_read_lock();
> - info.si_pid = task_pid_nr_ns(tsk, task_active_pid_ns(tsk->parent));
> - info.si_uid = from_kuid_munged(task_cred_xxx(tsk->parent, user_ns),
> + info.si_pid = task_pid_nr_ns(tsk, task_active_pid_ns(rcu_dereference(tsk->parent)));
> + info.si_uid = from_kuid_munged(task_cred_xxx(rcu_dereference(tsk->parent), user_ns),
> task_uid(tsk));
> rcu_read_unlock();
Still wrong because that access fundamentally depends upon the
task_list_lock no the rcu_read_lock. Things need to be consistent for
longer than the rcu_read_lock is held.
This patch makes sparse happy and confuses programmers who are trying to
read the code.
Eric
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next prev parent reply other threads:[~2020-02-05 23:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 17:24 [Linux-kernel-mentees] [PATCH] signal.c: Fix sparse warnings madhuparnabhowmik10
2020-02-05 22:59 ` Eric W. Biederman [this message]
2020-02-06 11:00 ` Madhuparna Bhowmik
2020-02-06 20:25 ` Joel Fernandes
2020-02-07 15:04 ` Madhuparna Bhowmik
-- strict thread matches above, loose matches on Subject: below --
2020-02-05 16:23 madhuparnabhowmik10
2020-02-05 16:51 ` Amol Grover
2020-02-05 17:09 ` Madhuparna Bhowmik
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