Commit 47fecca1 authored Oct 09, 2014 by Oleg Nesterov Committed by Linus Torvalds Oct 09, 2014

fs/proc/task_nommu.c: don't use priv->task->mm



I do not know if CONFIG_PREEMPT/SMP is possible without CONFIG_MMU
but the usage of task->mm in m_stop(). The task can exit/exec before
we take mmap_sem, in this case m_stop() can hit NULL or unlock the
wrong rw_semaphore.

Also, this code uses priv->task != NULL to decide whether we need
up_read/mmput. This is correct, but we will probably kill priv->task.
Change m_start/m_stop to rely on IS_ERR_OR_NULL() like task_mmu.c does.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 27692cd5

fs/proc/task_nommu.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -217,17 +217,17 @@ static void m_start(struct seq_file m, loff_t *pos)
		return ERR_PTR(-ESRCH);

		mm = priv->mm;
		if (!mm \|\| !atomic_inc_not_zero(&mm->mm_users)) {
		put_task_struct(priv->task);
		priv->task = NULL;
		if (!mm \|\| !atomic_inc_not_zero(&mm->mm_users))
		return NULL;
		}
		down_read(&mm->mmap_sem);

		down_read(&mm->mmap_sem);
		/* start from the Nth VMA */
		for (p = rb_first(&mm->mm_rb); p; p = rb_next(p))
		if (n-- == 0)
		return p;

		up_read(&mm->mmap_sem);
		mmput(mm);
		return NULL;
		}

		@@ -235,11 +235,13 @@ static void m_stop(struct seq_file m, void _vml)
		{
		struct proc_maps_private *priv = m->private;

		if (!IS_ERR_OR_NULL(_vml)) {
		up_read(&priv->mm->mmap_sem);
		mmput(priv->mm);
		}
		if (priv->task) {
		struct mm_struct *mm = priv->task->mm;
		up_read(&mm->mmap_sem);
		mmput(mm);
		put_task_struct(priv->task);
		priv->task = NULL;
		}
		}