[PATCH 6.18.y] mm/damon/core: disallow non-power of two min_region_sz on damon_start()

[SeongJae Park <sj@kernel.org>]

Commit d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region") introduced
a bug that allows unaligned DAMON region address ranges.  Commit
c80f46ac228b ("mm/damon/core: disallow non-power of two min_region_sz")
fixed it, but only for damon_commit_ctx() use case.  Still, DAMON sysfs
interface can emit non-power of two min_region_sz via damon_start().  Fix
the path by adding the is_power_of_2() check on damon_start().

The issue was discovered by sashiko [1].

Link: https://lore.kernel.org/20260411213638.77768-1-sj@kernel.org
Link: https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org [1]
Fixes: d8f867fa0825 ("mm/damon: add damon_ctx->min_sz_region")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 95093e5cb4c5b50a5b1a4b79f2942b62744bd66a)
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 87b6c9c2d647..e016ca7fde5e 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1352,6 +1352,11 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive)
 	int i;
 	int err = 0;
 
+	for (i = 0; i < nr_ctxs; i++) {
+		if (!is_power_of_2(ctxs[i]->min_sz_region))
+			return -EINVAL;
+	}
+
 	mutex_lock(&damon_lock);
 	if ((exclusive && nr_running_ctxs) ||
 			(!exclusive && running_exclusive_ctxs)) {
-- 
2.47.3