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Date: Tue, 5 Aug 2014 21:46:44 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Alexander Viro <viro@...iv.linux.org.uk>, Cyrill Gorcunov <gorcunov@...nvz.org>, David Howells <dhowells@...hat.com>, "David S. Miller" <davem@...emloft.net>, "Eric W. Biederman" <ebiederm@...ssion.com>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, "Kirill A. Shutemov" <kirill@...temov.name>, Peter Zijlstra <peterz@...radead.org>, Sasha Levin <levinsasha928@...il.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org Subject: [PATCH v2 1/7] 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@...hat.com> --- fs/proc/task_mmu.c | 8 +++----- 1 files changed, 3 insertions(+), 5 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index cfa63ee..8a5271e 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -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; } -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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