[PATCH v3 2/2] mm/damon/reclaim: validate min_region_size to be power of 2

[Liew Rui Yan <aethernet65535@gmail.com>]

The damon_commit_ctx() checks if 'min_region_sz' is a power-of-2.
However, if an invalid input is provided via the DAMON_RECLAIM interface,
the validation failure occurs too late, causing kdamond to terminate
unexpectedly.

To reproduce:
1. Enable DAMON_RECLAIM.
2. Set an invalid 'addr_unit' (e.g., addr_unit=3) so that
   'min_region_sz = DAMON_MIN_REGION_SZ / addr_unit' becomes
   non-power-of-2.
3. Commit parameters, and observe kdamond termination.

This patch adds an early check in damon_reclaim_apply_parameters() to
validate 'min_region_sz' and return -EINVAL immediately if it is not a
power-of-2, preventing unexpected kdamond termination.

Fixes: 7db551fcfb2a ("mm/damon/reclaim: support addr_unit for DAMON_RECLAIM")
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
---
 mm/damon/reclaim.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/damon/reclaim.c b/mm/damon/reclaim.c
index 86da14778658..2747eef5919d 100644
--- a/mm/damon/reclaim.c
+++ b/mm/damon/reclaim.c
@@ -204,6 +204,11 @@ static int damon_reclaim_apply_parameters(void)
 	param_ctx->addr_unit = addr_unit;
 	param_ctx->min_region_sz = max(DAMON_MIN_REGION_SZ / addr_unit, 1);
 
+	if (!is_power_of_2(param_ctx->min_region_sz)) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	if (!damon_reclaim_mon_attrs.aggr_interval) {
 		err = -EINVAL;
 		goto out;
-- 
2.53.0