linux-kernel - [PATCH] Huge TLB: Potential NULL deref in arch/x86/mm/hugetlbpage.c:huge_pmd

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Message-ID: <alpine.LNX.2.00.1102032142580.15101@swampdragon.chaosbits.net>
Date:	Thu, 3 Feb 2011 21:50:04 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	linux-kernel@...r.kernel.org
cc:	x86@...nel.org, linux-mm@...ck.org, Tejun Heo <tj@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rohit Seth <rohit.seth@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] Huge TLB: Potential NULL deref in
 arch/x86/mm/hugetlbpage.c:huge_pmd_share()

In arch/x86/mm/hugetlbpage.c:huge_pmd_share() we call find_vma(mm, addr) 
and then subsequently dereference the pointer returned without checking if 
it was NULL. I can't find anything that guarantees that find_vma() will 
never return NULL in this case, so I believe there's a genuine bug. 
However, I'd greatly appreciate it if someone would take the time to 
double check me.
This patch implements what I believe to be the correct handling of a NULL 
return from find_vma(). Please consider for inclusion.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 hugetlbpage.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 069ce7c..0ebd3d0 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -61,14 +61,19 @@ static int vma_shareable(struct vm_area_struct *vma, unsigned long addr)
 static void huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
 {
 	struct vm_area_struct *vma = find_vma(mm, addr);
-	struct address_space *mapping = vma->vm_file->f_mapping;
-	pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
-			vma->vm_pgoff;
+	struct address_space *mapping;
+	pgoff_t idx;
 	struct prio_tree_iter iter;
 	struct vm_area_struct *svma;
 	unsigned long saddr;
 	pte_t *spte = NULL;
 
+	if (!vma)
+		return;
+
+	mapping = vma->vm_file->f_mapping;
+	idx = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
+
 	if (!vma_shareable(vma, addr))
 		return;
 

-- 
Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.

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