[PATCH] mm/mempolicy: Fix memory leak in set_mempolicy_home_node system call

[Mathieu Desnoyers]

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@xxxxxxxxxxxx>
Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Feng Tang <feng.tang@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: <linux-api@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 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