[PATCH v2] mm/damon/sysfs: fix param_ctx leak on damon_sysfs_new_test_ctx() failure

[PATCH v2] mm/damon/sysfs: fix param_ctx leak on damon_sysfs_new_test_ctx() failure

[Josh Law]

When damon_sysfs_new_test_ctx() fails in damon_sysfs_commit_input(),
param_ctx is leaked because the early return skips the cleanup at the
out label. Destroy param_ctx before returning.

Fixes: f0c5118ebb0e ("mm/damon/sysfs: catch commit test ctx alloc failure")
Cc: <stable@vger.kernel.org> # 6.18.x
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index 576d1ddd736b..b573b9d60784 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1524,8 +1524,10 @@ static int damon_sysfs_commit_input(void *data)
 	if (IS_ERR(param_ctx))
 		return PTR_ERR(param_ctx);
 	test_ctx = damon_sysfs_new_test_ctx(kdamond->damon_ctx);
-	if (!test_ctx)
+	if (!test_ctx) {
+		damon_destroy_ctx(param_ctx);
 		return -ENOMEM;
+	}
 	err = damon_commit_ctx(test_ctx, param_ctx);
 	if (err)
 		goto out;
-- 
2.34.1

[PATCH v2] mm/damon/sysfs: check contexts->nr before accessing contexts_arr[0]

[Josh Law]

Multiple sysfs command paths dereference contexts_arr[0] without first
verifying that nr_contexts >= 1.  A user can set nr_contexts to 0 via
sysfs while DAMON is running, causing NULL pointer dereferences.

Guard all commands (except OFF) at the entry point of
damon_sysfs_handle_cmd().

Fixes: 0ac32b8affb5 ("mm/damon/sysfs: support DAMOS stats")
Cc: <stable@vger.kernel.org>	# 5.18.x
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index b573b9d60784..ddc30586c0e6 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1749,6 +1749,9 @@ static int damon_sysfs_update_schemes_tried_regions(
 static int damon_sysfs_handle_cmd(enum damon_sysfs_cmd cmd,
 		struct damon_sysfs_kdamond *kdamond)
 {
+	if (cmd != DAMON_SYSFS_CMD_OFF && kdamond->contexts->nr != 1)
+		return -EINVAL;
+
 	switch (cmd) {
 	case DAMON_SYSFS_CMD_ON:
 		return damon_sysfs_turn_damon_on(kdamond);
-- 
2.34.1

[PATCH v2] mm/damon/sysfs: check contexts->nr in repeat_call_fn

[Josh Law]

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.

Fixes: d809a7c64ba8 ("mm/damon/sysfs: implement refresh_ms file internal work")
Cc: <stable@vger.kernel.org> # 6.17.x
Signed-off-by: Josh Law <objecting@objecting.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/sysfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index ddc30586c0e6..6a44a2f3d8fc 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1620,9 +1620,12 @@ static int damon_sysfs_repeat_call_fn(void *data)
 
 	if (!mutex_trylock(&damon_sysfs_lock))
 		return 0;
+	if (sysfs_kdamond->contexts->nr != 1)
+		goto out;
 	damon_sysfs_upd_tuned_intervals(sysfs_kdamond);
 	damon_sysfs_upd_schemes_stats(sysfs_kdamond);
 	damon_sysfs_upd_schemes_effective_quotas(sysfs_kdamond);
+out:
 	mutex_unlock(&damon_sysfs_lock);
 	return 0;
 }
-- 
2.34.1

Re: [PATCH v2] mm/damon/sysfs: fix param_ctx leak on damon_sysfs_new_test_ctx() failure

[SeongJae Park]

Apparently this series is only by a mistake, and therefore a new version [1] is
posted.  So I will skip this series and review the new version.  Let me know if
anything is wrong.

[1] https://lore.kernel.org/20260320163559.178101-1-objecting@objecting.org


Thanks,
SJ

[...]

Re: [PATCH v2] mm/damon/sysfs: fix param_ctx leak on damon_sysfs_new_test_ctx() failure

[Josh Law]

On 21 March 2026 00:02:54 GMT, SeongJae Park <sj@kernel.org> wrote:
>Apparently this series is only by a mistake, and therefore a new version [1] is
>posted.  So I will skip this series and review the new version.  Let me know if
>anything is wrong.
>
>[1] https://lore.kernel.org/20260320163559.178101-1-objecting@objecting.org
>
>
>Thanks,
>SJ
>
>[...]


Only the numbering was wrong, like no 1/3 2/3 etc. Im a bit of a perferctionist so i nitpicked it

V/R

Josh Law