linux-kernel - [Patch] proc: check error pointer returned by m

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Date:	Mon, 28 Mar 2011 11:46:38 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	WANG Cong <xiyou.wangcong@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric B Munson <emunson@...bm.net>,
	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>
Subject: [Patch] proc: check error pointer returned by m_start()

Anca reported a bug:

[15117.080119] BUG: unable to handle kernel paging request at fffffffffffffff3
[15117.080152] IP: [<ffffffff811b4989>] vma_stop+0x19/0x40

Linus did the initial analysis, and found this was caused
by commit ec6fd8a4355c ("report errors in /proc/*/*map*
sanely"), which replaces NULL with various ERR_PTR() cases.

This is true, that commit changed the return value of m_start(),
which will return an error pointer on failure, but Al forgot
to check the error pointer in m_stop() which will be called
when m_start() fails. This patches fixes it.

Reported-by: Anca Emanuel <anca.emanuel@...il.com>
Tested-by: Anca Emanuel <anca.emanuel@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: WANG Cong <xiyou.wangcong@...il.com>

---
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 7c708a4..6b82632 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -90,7 +90,7 @@ static void pad_len_spaces(struct seq_file *m, int len)
 
 static void vma_stop(struct proc_maps_private *priv, struct vm_area_struct *vma)
 {
-	if (vma && vma != priv->tail_vma) {
+	if (vma && !IS_ERR(vma) && vma != priv->tail_vma) {
 		struct mm_struct *mm = vma->vm_mm;
 		up_read(&mm->mmap_sem);
 		mmput(mm);
--
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