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mm/damon/sysfs: check contexts->nr in repeat_call_fn 

damon_sysfs_repeat_call_fn() calls damon_sysfs_upd_tuned_intervals(),
damon_sysfs_upd_schemes_stats(), and
damon_sysfs_upd_schemes_effective_quotas() without checking contexts->nr. 
If nr_contexts is set to 0 via sysfs while DAMON is running, these
functions dereference contexts_arr[0] and cause a NULL pointer
dereference.  Add the missing check.

For example, the issue can be reproduced using DAMON sysfs interface and
DAMON user-space tool (damo) [1] like below.

    $ sudo damo start --refresh_interval 1s
    $ echo 0 | sudo tee \
            /sys/kernel/mm/damon/admin/kdamonds/0/contexts/nr_contexts

Link: https://patch.msgid.link/20260320163559.178101-3-objecting@objecting.org
Link: https://lkml.kernel.org/r/20260321175427.86000-4-sj@kernel.org
Link: https://github.com/damonitor/damo [1]
Fixes: d809a7c64b ("mm/damon/sysfs: implement refresh_ms file internal work")
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.17+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Josh Law 2026-03-21 10:54:26 -07:00 committed by Andrew Morton
parent 1bfe9fb5ed
commit 6557004a8b
1 changed files with 3 additions and 0 deletions
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3
mm/damon/sysfs.c
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@ -1620,9 +1620,12 @@ static int damon_sysfs_repeat_call_fn(void *data)
if (!mutex_trylock(&damon_sysfs_lock)) if (!mutex_trylock(&damon_sysfs_lock))
return 0; return 0;
if (sysfs_kdamond->contexts->nr != 1)
goto out;
damon_sysfs_upd_tuned_intervals(sysfs_kdamond); damon_sysfs_upd_tuned_intervals(sysfs_kdamond);
damon_sysfs_upd_schemes_stats(sysfs_kdamond); damon_sysfs_upd_schemes_stats(sysfs_kdamond);
damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond); damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond);
out:
mutex_unlock(&damon_sysfs_lock); mutex_unlock(&damon_sysfs_lock);
return 0; return 0;
} }