[PATCH 1/2] 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.

[ Mathieu: compile-tested only. Tested-by would be welcome. ]

Fixes: c6018b4b2549 ("mm/mempolicy: add set_mempolicy_home_node syscall")
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Randy Dunlap <redacted>
Reviewed-by: "Huang, Ying" <redacted>
Reviewed-by: Aneesh Kumar K.V <redacted>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Aneesh Kumar K.V <redacted>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Feng Tang <redacted>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andrea Arcangeli <redacted>
Cc: Mel Gorman <redacted>
Cc: Mike Kravetz <redacted>
Cc: Randy Dunlap <redacted>
Cc: Vlastimil Babka <redacted>
Cc: Andi Kleen <redacted>
Cc: Dan Williams <redacted>
Cc: Huang Ying <redacted>
Cc: linux-api@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: stable@vger.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