From: Oleg Nesterov <oleg@redhat.com>
To: Christopher Yeoh <cyeoh@au1.ibm.com>
Cc: linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
David Howells <dhowells@redhat.com>
Subject: Re: [PATCH] Fix race in process_vm_rw_core
Date: Mon, 16 Jan 2012 19:59:24 +0100 [thread overview]
Message-ID: <20120116185924.GA24418@redhat.com> (raw)
In-Reply-To: <20120116135655.1a31e13c@rockpopper>
On 01/16, Christopher Yeoh wrote:
>
> +struct mm_struct *get_check_task_mm(struct task_struct *task, unsigned int mode)
> +{
> + struct mm_struct *mm;
> + int err;
> +
> + err = mutex_lock_killable(&task->signal->cred_guard_mutex);
> + if (err)
> + return ERR_PTR(err);
> +
> + task_lock(task);
> + mm = task->mm;
> + if (mm != current->mm && __ptrace_may_access(task, mode)) {
> + mm = ERR_PTR(-EACCES);
> + goto out;
> + }
> +
> + if (mm) {
> + if (task->flags & PF_KTHREAD)
> + mm = NULL;
> + else
> + atomic_inc(&mm->mm_users);
> + }
This still looks a bit strange, we call __ptrace_may_access()
before we check ->mm != NULL even if this is safe... Really, we
would simply fix the bug then try to microoptimize this code.
But OK, I promised I won't argue ;)
I believe the patch is correct and fixes the problem.
Oleg.
next prev parent reply other threads:[~2012-01-16 19:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-13 11:30 [PATCH] Fix race in process_vm_rw_core Christopher Yeoh
2012-01-13 16:04 ` Oleg Nesterov
2012-01-13 23:26 ` Christopher Yeoh
2012-01-14 17:58 ` Oleg Nesterov
2012-01-16 2:56 ` Christopher Yeoh
2012-01-16 18:59 ` Oleg Nesterov [this message]
2012-01-13 22:30 ` Andrew Morton
2012-01-13 23:30 ` Christopher Yeoh
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