linux-kernel - Re: [RFC PATCH] mm/mempolicy: Fix memory leak in set_mempolicy_home

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Message-ID: <Y5rR9n5HSvlATV5A@dhcp22.suse.cz>
Date:   Thu, 15 Dec 2022 08:51:18 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Feng Tang <feng.tang@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Huang Ying <ying.huang@...el.com>, linux-api@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [RFC PATCH] mm/mempolicy: Fix memory leak in
 set_mempolicy_home_node system call

On Wed 14-12-22 17:21:10, Mathieu Desnoyers wrote:
> When encountering any vma in the range with policy other than MPOL_BIND
> or MPOL_PREFERRED_MANY, an error is returned without issuing a mpol_put
> on the policy just allocated with mpol_dup().
> 
> This allows arbitrary users to leak kernel memory.
> 
> Fixes: c6018b4b2549 ("mm/mempolicy: add set_mempolicy_home_node syscall")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Cc: Ben Widawsky <ben.widawsky@...el.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Feng Tang <feng.tang@...el.com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: <linux-api@...r.kernel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: stable@...r.kernel.org # 5.17+

Acked-by: Michal Hocko <mhocko@...e.com>
Thanks for catching this!

Btw. looking at the code again it seems rather pointless to duplicate
the policy just to throw it away anyway. A slightly bigger diff but this
looks more reasonable to me. What do you think? I can also send it as a
clean up on top of your fix.
---
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 61aa9aedb728..918cdc8a7f0c 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1489,7 +1489,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 {
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma;
-	struct mempolicy *new;
+	struct mempolicy *new. *old;
 	unsigned long vmstart;
 	unsigned long vmend;
 	unsigned long end;
@@ -1521,30 +1521,28 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 		return 0;
 	mmap_write_lock(mm);
 	for_each_vma_range(vmi, vma, end) {
-		vmstart = max(start, vma->vm_start);
-		vmend   = min(end, vma->vm_end);
-		new = mpol_dup(vma_policy(vma));
-		if (IS_ERR(new)) {
-			err = PTR_ERR(new);
-			break;
-		}
-		/*
-		 * Only update home node if there is an existing vma policy
-		 */
-		if (!new)
-			continue;
-
 		/*
 		 * If any vma in the range got policy other than MPOL_BIND
 		 * or MPOL_PREFERRED_MANY we return error. We don't reset
 		 * the home node for vmas we already updated before.
 		 */
-		if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
+		old = vma_policy(vma);
+		if (!old)
+			continue;
+		if (old->mode != MPOL_BIND && old->mode != MPOL_PREFERRED_MANY) {
 			err = -EOPNOTSUPP;
 			break;
 		}
 
+		new = mpol_dup(vma_policy(vma));
+		if (IS_ERR(new)) {
+			err = PTR_ERR(new);
+			break;
+		}
+
 		new->home_node = home_node;
+		vmstart = max(start, vma->vm_start);
+		vmend   = min(end, vma->vm_end);
 		err = mbind_range(mm, vmstart, vmend, new);
 		mpol_put(new);
 		if (err)
-- 
Michal Hocko
SUSE Labs