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

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Date:   Wed, 14 Dec 2022 17:21:10 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "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>,
        Michal Hocko <mhocko@...nel.org>,
        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: [RFC PATCH] mm/mempolicy: Fix memory leak in set_mempolicy_home_node system call

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+
---
 mm/mempolicy.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 61aa9aedb728..02c8a712282f 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1540,6 +1540,7 @@ SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, le
 		 * the home node for vmas we already updated before.
 		 */
 		if (new->mode != MPOL_BIND && new->mode != MPOL_PREFERRED_MANY) {
+			mpol_put(new);
 			err = -EOPNOTSUPP;
 			break;
 		}
-- 
2.25.1