[PATCH 0/2] mm/damon/core: fix unitialized memory error from

[PATCH 0/2] mm/damon/core: fix unitialized memory error from

[SeongJae Park]

damos_new_filter() is returning a damos_filter struct without
initializing its ->list field.  And the users of the function uses the
struct without initializing the field.  As a result, uninitialized
memory access error is possible.  Actually, a kernel NULL pointer
dereference BUG can be triggered using DAMON user-space tool, like
below.

    # damo start --damos_action stat --damos_filter anon matching
    # damo tune --damos_action stat --damos_filter anon matching --damos_filter anon nomatching
    # dmesg
    [...]
    [   36.908136] BUG: kernel NULL pointer dereference, address: 0000000000000008
    [   36.910483] #PF: supervisor write access in kernel mode
    [   36.912238] #PF: error_code(0x0002) - not-present page
    [   36.913415] PGD 0 P4D 0
    [   36.913978] Oops: 0002 [#1] PREEMPT SMP PTI
    [   36.914878] CPU: 32 PID: 1335 Comm: kdamond.0 Not tainted 6.5.0-rc3-mm-unstable-damon+ #1
    [   36.916621] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
    [   36.919051] RIP: 0010:damos_destroy_filter (include/linux/list.h:114 include/linux/list.h:137 include/linux/list.h:148 mm/damon/core.c:345 mm/damon/core.c:355)
    [...]
    [   36.938247] Call Trace:
    [   36.938721]  <TASK>
    [...]
    [   36.950064] ? damos_destroy_filter (include/linux/list.h:114 include/linux/list.h:137 include/linux/list.h:148 mm/damon/core.c:345 mm/damon/core.c:355)
    [   36.950883] ? damon_sysfs_set_scheme_filters.isra.0 (mm/damon/sysfs-schemes.c:1573)
    [   36.952019] damon_sysfs_set_schemes (mm/damon/sysfs-schemes.c:1674 mm/damon/sysfs-schemes.c:1686)
    [   36.952875] damon_sysfs_apply_inputs (mm/damon/sysfs.c:1312 mm/damon/sysfs.c:1298)
    [   36.953757] ? damon_pa_check_accesses (mm/damon/paddr.c:168 mm/damon/paddr.c:179)
    [   36.954648] damon_sysfs_cmd_request_callback (mm/damon/sysfs.c:1329 mm/damon/sysfs.c:1359)
    [...]

The first patch of this patchset fixes the bug by initializing the field in
damos_new_filter().  The second patch adds a unit test for the problem.
Note that the second patch Cc stable@ without Fixes: tag, since it would
be better to be ingested together for avoiding any future regression.

SeongJae Park (2):
  mm/damon/core: initialize damo_filter->list from damos_new_filter()
  mm/damon/core-test: add a test for damos_new_filter()

 mm/damon/core-test.h | 13 +++++++++++++
 mm/damon/core.c      |  1 +
 2 files changed, 14 insertions(+)

-- 
2.25.1

[PATCH 1/2] mm/damon/core: initialize damo_filter->list from damos_new_filter()

[SeongJae Park]

damos_new_filter() is not initializing the list field of newly allocated
filter object.  However, DAMON sysfs interface and DAMON_RECLAIM are not
initializing it after calling damos_new_filter().  As a result,
accessing uninitialized memory is possible.  Actually, adding multiple
DAMOS filters via DAMON sysfs interface caused NULL pointer
dereferencing.  Initialize the field just after the allocation from
damos_new_filter().

Fixes: 98def236f63c ("mm/damon/core: implement damos filter")
Cc: stable@vger.kernel.org # 6.3.x-
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 91cff7f2997e..eb9580942a5c 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -273,6 +273,7 @@ struct damos_filter *damos_new_filter(enum damos_filter_type type,
 		return NULL;
 	filter->type = type;
 	filter->matching = matching;
+	INIT_LIST_HEAD(&filter->list);
 	return filter;
 }
 
-- 
2.25.1

[PATCH 2/2] mm/damon/core-test: add a test for damos_new_filter()

[SeongJae Park]

damos_new_filter() was having a bug that not initializing ->list field
of the returning damos_filter struct, which results in access to
uninitialized memory.  Add a unit test for the function.

Cc: stable@vger.kernel.org # 6.3.x-
Signed-off-by: SeongJae Park <sj@kernel.org>
---
 mm/damon/core-test.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/damon/core-test.h b/mm/damon/core-test.h
index bb07721909e1..4bddbfe243c3 100644
--- a/mm/damon/core-test.h
+++ b/mm/damon/core-test.h
@@ -341,6 +341,18 @@ static void damon_test_set_attrs(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, damon_set_attrs(c, &invalid_attrs), -EINVAL);
 }
 
+static void damos_test_new_filter(struct kunit *test)
+{
+	struct damos_filter *filter;
+
+	filter = damos_new_filter(DAMOS_FILTER_TYPE_ANON, true);
+	KUNIT_EXPECT_EQ(test, filter->type, DAMOS_FILTER_TYPE_ANON);
+	KUNIT_EXPECT_EQ(test, filter->matching, true);
+	KUNIT_EXPECT_PTR_EQ(test, filter->list.prev, &filter->list);
+	KUNIT_EXPECT_PTR_EQ(test, filter->list.next, &filter->list);
+	damos_destroy_filter(filter);
+}
+
 static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_target),
 	KUNIT_CASE(damon_test_regions),
@@ -353,6 +365,7 @@ static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_set_regions),
 	KUNIT_CASE(damon_test_update_monitoring_result),
 	KUNIT_CASE(damon_test_set_attrs),
+	KUNIT_CASE(damos_test_new_filter),
 	{},
 };
 
-- 
2.25.1