fs/proc/task_mmu.c: don't use task->mm in m_start() and show_*map() (46c298cf) · Commits · 戴 / test

get_gate_vma(priv->task->mm) looks ugly and wrong, task->mm can be NULL or it can changed by exec right after mm_access(). And in theory this race is not harmless, the task can exec and then later exit and free the new mm_struct. In this case get_task_mm(oldmm) can't help, get_gate_vma(task->mm) can read the freed/unmapped memory. I think that priv->task should simply die and hold_task_mempolicy() logic can be simplified. tail_vma logic asks for cleanups too. Signed-off-by:

Oleg Nesterov <oleg@redhat.com> Acked-by:

Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by:

Cyrill Gorcunov <gorcunov@openvz.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/task_mmu.c

+3 −5

Original line number	Diff line number	Diff line
		@@ -170,7 +170,7 @@ static void m_start(struct seq_file m, loff_t *pos)
		return mm;
		down_read(&mm->mmap_sem);

		tail_vma = get_gate_vma(priv->task->mm);
		tail_vma = get_gate_vma(mm);
		priv->tail_vma = tail_vma;
		hold_task_mempolicy(priv);
		/* Start with last addr hint */
		@@ -351,12 +351,11 @@ static int show_map(struct seq_file m, void v, int is_pid)
		{
		struct vm_area_struct *vma = v;
		struct proc_maps_private *priv = m->private;
		struct task_struct *task = priv->task;

		show_map_vma(m, vma, is_pid);

		if (m->count < m->size) /* vma is copied successfully */
		m->version = (vma != get_gate_vma(task->mm))
		m->version = (vma != priv->tail_vma)
		? vma->vm_start : 0;
		return 0;
		}
		@@ -584,7 +583,6 @@ static void show_smap_vma_flags(struct seq_file m, struct vm_area_struct vma)
		static int show_smap(struct seq_file m, void v, int is_pid)
		{
		struct proc_maps_private *priv = m->private;
		struct task_struct *task = priv->task;
		struct vm_area_struct *vma = v;
		struct mem_size_stats mss;
		struct mm_walk smaps_walk = {
		@@ -639,7 +637,7 @@ static int show_smap(struct seq_file m, void v, int is_pid)
		show_smap_vma_flags(m, vma);

		if (m->count < m->size) /* vma is copied successfully */
		m->version = (vma != get_gate_vma(task->mm))
		m->version = (vma != priv->tail_vma)
		? vma->vm_start : 0;
		return 0;
		}

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