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.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: c6018b4 ("mm/mempolicy: add set_mempolicy_home_node syscall")
Signed-off-by: Mathieu Desnoyers <[email protected]>
Reviewed-by: Randy Dunlap <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Reviewed-by: Aneesh Kumar K.V <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Feng Tang <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: <[email protected]>	[5.17+]
Signed-off-by: Andrew Morton <[email protected]>

Author: compudj

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;
 		}