mm/damon/sysfs-schemes: skip stats update if the scheme directory is removed

A DAMON sysfs interface user can start DAMON with a scheme, remove the
sysfs directory for the scheme, and then ask update of the scheme's stats.
Because the schemes stats update logic isn't aware of the situation, it
results in an invalid memory access.  Fix the bug by checking if the
scheme sysfs directory exists.

Link: https://lkml.kernel.org/r/20221114175552.1951-1-sj@kernel.org
Fixes: 0ac32b8affb5 ("mm/damon/sysfs: support DAMOS stats")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[v5.18]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 9f1219a67e3f17bf49794581fa266f6b45782d59..5ce403378c2000bb827e72cb38c8c54ce616044c 100644 (file)
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -2339,6 +2339,10 @@ static int damon_sysfs_upd_schemes_stats(struct damon_sysfs_kdamond *kdamond)
        damon_for_each_scheme(scheme, ctx) {
                struct damon_sysfs_stats *sysfs_stats;
 
+               /* user could have removed the scheme sysfs dir */
+               if (schemes_idx >= sysfs_schemes->nr)
+                       break;
+
                sysfs_stats = sysfs_schemes->schemes_arr[schemes_idx++]->stats;
                sysfs_stats->nr_tried = scheme->stat.nr_tried;
                sysfs_stats->sz_tried = scheme->stat.sz_tried;