fs/proc/task_mmu.c: don't use task->mm in m_start() and show_*map()
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>
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@ -170,7 +170,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
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return mm;
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down_read(&mm->mmap_sem);
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tail_vma = get_gate_vma(priv->task->mm);
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tail_vma = get_gate_vma(mm);
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priv->tail_vma = tail_vma;
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hold_task_mempolicy(priv);
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/* Start with last addr hint */
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@ -351,12 +351,11 @@ static int show_map(struct seq_file *m, void *v, int is_pid)
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{
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struct vm_area_struct *vma = v;
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struct proc_maps_private *priv = m->private;
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struct task_struct *task = priv->task;
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show_map_vma(m, vma, is_pid);
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if (m->count < m->size) /* vma is copied successfully */
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m->version = (vma != get_gate_vma(task->mm))
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m->version = (vma != priv->tail_vma)
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? vma->vm_start : 0;
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return 0;
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}
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@ -584,7 +583,6 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
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static int show_smap(struct seq_file *m, void *v, int is_pid)
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{
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struct proc_maps_private *priv = m->private;
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struct task_struct *task = priv->task;
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struct vm_area_struct *vma = v;
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struct mem_size_stats mss;
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struct mm_walk smaps_walk = {
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@ -639,7 +637,7 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
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show_smap_vma_flags(m, vma);
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if (m->count < m->size) /* vma is copied successfully */
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m->version = (vma != get_gate_vma(task->mm))
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m->version = (vma != priv->tail_vma)
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? vma->vm_start : 0;
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return 0;
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}
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