mm: fix NULL ptr deref when walking hugepages
Sasha Levin [Tue, 29 May 2012 22:06:15 +0000 (15:06 -0700)]
commit 08fa29d916c6e271ad13978cd993e7238c68db97 upstream.

A missing validation of the value returned by find_vma() could cause a
NULL ptr dereference when walking the pagetable.

This is triggerable from usermode by a simple user by trying to read a
page info out of /proc/pid/pagemap which doesn't exist.

Introduced by commit 025c5b2451e4 ("thp: optimize away unnecessary page
table locking").

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/proc/task_mmu.c

index 1030a71..7faaf2a 100644 (file)
@@ -784,7 +784,7 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 
        /* find the first VMA at or above 'addr' */
        vma = find_vma(walk->mm, addr);
-       if (pmd_trans_huge_lock(pmd, vma) == 1) {
+       if (vma && pmd_trans_huge_lock(pmd, vma) == 1) {
                for (; addr != end; addr += PAGE_SIZE) {
                        unsigned long offset;