[RFC PATCH 0/8] mm/damon: move damos filter range arguments validation to core

[RFC PATCH 0/8] mm/damon: move damos filter range arguments validation to core

[SJ Park]

DAMOS filter range arguments are being validated in the DAMON sysfs
interface.  Some of those have minor time-of-check to time-of-use
(TOCTOU) bugs.  In future, other callers might have duplicated
validations with similar bugs.

Fix the bugs and further refactor the code to move the validation to the
core layer.  Also add kunit test cases for the validations.

Patches 1 and 2 fix the existing TOCTOU bugs.  Patches 3 and 4 adds the
validation in the core layer.  Patch 5 drops the replicated validation
in DAMON sysfs interface.  Patch 6 further cleanup the code.  Patches 7
and 8 extends kunit tests to test the validation.

SJ Park (8):
  mm/damon/sysfs-schemes: read sysfs_filter->addr_range only once
  mm/damon/sysfs-schemes: read sysfs_filter->sz_range only once
  mm/damon/core: return an error from damos_commit_filter_arg()
  mm/damon/core: disallow max < min damos filter range arguments commit
  mm/damon/sysfs-schemes: drop centralized filter range arg validations
  mm/damon/sysfs-schemes: use switch-case in add_scheme_filters()
  mm/damon/core-kunit: extend damos_commit_filter_for() for wrong input
  mm/damon/core-kunit: test invalid damos filter commits

 mm/damon/core.c             | 24 ++++++++++++++++-------
 mm/damon/sysfs-schemes.c    | 32 +++++++++++++------------------
 mm/damon/tests/core-kunit.h | 38 ++++++++++++++++++++++++++++---------
 3 files changed, 59 insertions(+), 35 deletions(-)


base-commit: ec1b9fab95fbfd9c5dbdfb841d91929c2cb63518
-- 
2.47.3

[RFC PATCH 1/8] mm/damon/sysfs-schemes: read sysfs_filter->addr_range only once

[SJ Park]

DAMON sysfs interface reads the user-provided address range arguments
for addr type DAMOS filter twice.  Once for validation, and once again
for assignments to the variable that will be passed to the core
layer. If the user updates the argument in parallel, an invalid address
range could be passed to the core layer.  Avoid it by doing the
assignments first, and then validating the assigned variables before
passing those to the core layer.

User impact of the bug should be trivial.  From the core layer's
perspective, the invalid address range is not really invalid.  It just
works as having a weird address range.  No critical issues such as a
crash or a leak could happen.  And sane users ain't do such parallel
arguments update anyway.  If they do, such racy behavior is arguably
somewhat expected and deserved.  That said, there is no reason to keep
such races.

Fixes: 2f1abcfccd86 ("mm/damon/sysfs-schemes: support address range type DAMOS filter")
Cc: <stable@vger.kernel.org> # 6.6.x
Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 3de4d804e049f..3c1c1cb387fec 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2831,12 +2831,12 @@ static int damon_sysfs_add_scheme_filters(struct damos *scheme,
 				return err;
 			}
 		} else if (filter->type == DAMOS_FILTER_TYPE_ADDR) {
-			if (sysfs_filter->addr_range.end <
-					sysfs_filter->addr_range.start) {
+			filter->addr_range = sysfs_filter->addr_range;
+			if (filter->addr_range.end <
+					filter->addr_range.start) {
 				damos_destroy_filter(filter);
 				return -EINVAL;
 			}
-			filter->addr_range = sysfs_filter->addr_range;
 		} else if (filter->type == DAMOS_FILTER_TYPE_TARGET) {
 			filter->target_idx = sysfs_filter->target_idx;
 		} else if (filter->type == DAMOS_FILTER_TYPE_HUGEPAGE_SIZE) {
-- 
2.47.3

[RFC PATCH 2/8] mm/damon/sysfs-schemes: read sysfs_filter->sz_range only once

[SJ Park]

DAMON sysfs interface reads the user-provided size range arguments for
hugepage_size type DAMOS filter twice.  Once for validation, and once
again for assignments to the variable that will be passed to the core
layer.  If the user updates the arguments in parallel, an invalid size
range could be passed to the core layer.  Avoid it by doing the
assignments first, and then validating the assigned variables before
passing those to the core layer.

User impact of the bug should be trivial.  From the core layer's
perspective, the invalid size range is not really invalid.  It just
works as having a weird size range.  No critical issues such as a crash
or a leak could happen.  And sane users ain't do such parallel arguments
update anyway.  If they do, such racy behavior is arguably somewhat
expected and deserved.  That said, there is no reason to keep such
races.

Fixes: ea1f204ba29a ("mm/damon/sysfs-schemes: add files for setting damos_filter->sz_range")
Cc: <stable@vger.kernel.org> # 6.15.x
Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 3c1c1cb387fec..8c8ab82c8facc 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2840,13 +2840,12 @@ static int damon_sysfs_add_scheme_filters(struct damos *scheme,
 		} else if (filter->type == DAMOS_FILTER_TYPE_TARGET) {
 			filter->target_idx = sysfs_filter->target_idx;
 		} else if (filter->type == DAMOS_FILTER_TYPE_HUGEPAGE_SIZE) {
-			if (sysfs_filter->range_min >
-					sysfs_filter->range_max) {
+			filter->sz_range.min = sysfs_filter->range_min;
+			filter->sz_range.max = sysfs_filter->range_max;
+			if (filter->range_min > filter->range_max) {
 				damos_destroy_filter(filter);
 				return -EINVAL;
 			}
-			filter->sz_range.min = sysfs_filter->range_min;
-			filter->sz_range.max = sysfs_filter->range_max;
 		} else if (filter->type == DAMOS_FILTER_TYPE_PROBE_HITS_WSUM) {
 			filter->range_min = sysfs_filter->range_min;
 			filter->range_max = sysfs_filter->range_max;
-- 
2.47.3

[RFC PATCH 3/8] mm/damon/core: return an error from damos_commit_filter_arg()

[SJ Park]

damos_commit_filter_arg() is supposed to always succeed.  It may not in
future, for example, if the given filter is invalid.  Prepare the case
by modifying its signature to return an error when it failed.  Also pipe
the return value to its callers and let them handle the error.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 0c98f7e267d07..3ad1fb2f21f3f 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1317,7 +1317,7 @@ static struct damos_filter *damos_nth_ops_filter(int n, struct damos *s)
 	return NULL;
 }
 
-static void damos_commit_filter_arg(
+static int damos_commit_filter_arg(
 		struct damos_filter *dst, struct damos_filter *src)
 {
 	switch (dst->type) {
@@ -1340,28 +1340,32 @@ static void damos_commit_filter_arg(
 	default:
 		break;
 	}
+	return 0;
 }
 
-static void damos_commit_filter(
+static int damos_commit_filter(
 		struct damos_filter *dst, struct damos_filter *src)
 {
 	dst->type = src->type;
 	dst->matching = src->matching;
 	dst->allow = src->allow;
-	damos_commit_filter_arg(dst, src);
+	return damos_commit_filter_arg(dst, src);
 }
 
 static int damos_commit_core_filters(struct damos *dst, struct damos *src)
 {
 	struct damos_filter *dst_filter, *next, *src_filter, *new_filter;
-	int i = 0, j = 0;
+	int i = 0, j = 0, err;
 
 	damos_for_each_core_filter_safe(dst_filter, next, dst) {
 		src_filter = damos_nth_core_filter(i++, src);
-		if (src_filter)
-			damos_commit_filter(dst_filter, src_filter);
-		else
+		if (src_filter) {
+			err = damos_commit_filter(dst_filter, src_filter);
+			if (err)
+				return err;
+		} else {
 			damos_destroy_filter(dst_filter);
+		}
 	}
 
 	damos_for_each_core_filter_safe(src_filter, next, src) {
-- 
2.47.3

[RFC PATCH 4/8] mm/damon/core: disallow max < min damos filter range arguments commit

[SJ Park]

damos_commit_filter_arg() receives range arguments for a few types of
DAMOS filters.  It allows any range including max < min range.  It is
fine for the logic, but makes no sense to support it.  Actually DAMON
sysfs interface is doing the validation on its own.  To avoid duplicated
validations in multiple DAMON API callers, it would be better to do the
validation in the core layer.  Add a validation of the given range.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 3ad1fb2f21f3f..3dec1a8f7ed3a 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1325,15 +1325,21 @@ static int damos_commit_filter_arg(
 		dst->memcg_id = src->memcg_id;
 		break;
 	case DAMOS_FILTER_TYPE_ADDR:
+		if (src->addr_range.end < src->addr_range.start)
+			return -EINVAL;
 		dst->addr_range = src->addr_range;
 		break;
 	case DAMOS_FILTER_TYPE_TARGET:
 		dst->target_idx = src->target_idx;
 		break;
 	case DAMOS_FILTER_TYPE_HUGEPAGE_SIZE:
+		if (src->sz_range.max < src->sz_range.min)
+			return -EINVAL;
 		dst->sz_range = src->sz_range;
 		break;
 	case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:
+		if (src->range_max < src->range_min)
+			return -EINVAL;
 		dst->range_min = src->range_min;
 		dst->range_max = src->range_max;
 		break;
-- 
2.47.3

[RFC PATCH 5/8] mm/damon/sysfs-schemes: drop centralized filter range arg validations

[SJ Park]

DAMON sysfs interface is validating wrong range arguments for DAMOS
filters.  Now the core layer is doing the same validation.  Drop the
duplicated validation in DAMON sysfs interface.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index 8c8ab82c8facc..a4ec5d54cfbd1 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2832,27 +2832,14 @@ static int damon_sysfs_add_scheme_filters(struct damos *scheme,
 			}
 		} else if (filter->type == DAMOS_FILTER_TYPE_ADDR) {
 			filter->addr_range = sysfs_filter->addr_range;
-			if (filter->addr_range.end <
-					filter->addr_range.start) {
-				damos_destroy_filter(filter);
-				return -EINVAL;
-			}
 		} else if (filter->type == DAMOS_FILTER_TYPE_TARGET) {
 			filter->target_idx = sysfs_filter->target_idx;
 		} else if (filter->type == DAMOS_FILTER_TYPE_HUGEPAGE_SIZE) {
 			filter->sz_range.min = sysfs_filter->range_min;
 			filter->sz_range.max = sysfs_filter->range_max;
-			if (filter->range_min > filter->range_max) {
-				damos_destroy_filter(filter);
-				return -EINVAL;
-			}
 		} else if (filter->type == DAMOS_FILTER_TYPE_PROBE_HITS_WSUM) {
 			filter->range_min = sysfs_filter->range_min;
 			filter->range_max = sysfs_filter->range_max;
-			if (filter->range_min > filter->range_max) {
-				damos_destroy_filter(filter);
-				return -EINVAL;
-			}
 		}
 
 		damos_add_filter(scheme, filter);
-- 
2.47.3

[RFC PATCH 6/8] mm/damon/sysfs-schemes: use switch-case in add_scheme_filters()

[SJ Park]

damon_sysfs_add_scheeme_filters() has long if-else chains for DAMOS
filter types.  Convert the code to use switch-case, which would be
cleaner and more efficient.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/sysfs-schemes.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
index a4ec5d54cfbd1..bfb6f0bc3f213 100644
--- a/mm/damon/sysfs-schemes.c
+++ b/mm/damon/sysfs-schemes.c
@@ -2822,7 +2822,8 @@ static int damon_sysfs_add_scheme_filters(struct damos *scheme,
 
 		if (!filter)
 			return -ENOMEM;
-		if (filter->type == DAMOS_FILTER_TYPE_MEMCG) {
+		switch (filter->type) {
+		case DAMOS_FILTER_TYPE_MEMCG:
 			err = damon_sysfs_memcg_path_to_id(
 					sysfs_filter->memcg_path,
 					&filter->memcg_id);
@@ -2830,16 +2831,23 @@ static int damon_sysfs_add_scheme_filters(struct damos *scheme,
 				damos_destroy_filter(filter);
 				return err;
 			}
-		} else if (filter->type == DAMOS_FILTER_TYPE_ADDR) {
+			break;
+		case DAMOS_FILTER_TYPE_ADDR:
 			filter->addr_range = sysfs_filter->addr_range;
-		} else if (filter->type == DAMOS_FILTER_TYPE_TARGET) {
+			break;
+		case DAMOS_FILTER_TYPE_TARGET:
 			filter->target_idx = sysfs_filter->target_idx;
-		} else if (filter->type == DAMOS_FILTER_TYPE_HUGEPAGE_SIZE) {
+			break;
+		case DAMOS_FILTER_TYPE_HUGEPAGE_SIZE:
 			filter->sz_range.min = sysfs_filter->range_min;
 			filter->sz_range.max = sysfs_filter->range_max;
-		} else if (filter->type == DAMOS_FILTER_TYPE_PROBE_HITS_WSUM) {
+			break;
+		case DAMOS_FILTER_TYPE_PROBE_HITS_WSUM:
 			filter->range_min = sysfs_filter->range_min;
 			filter->range_max = sysfs_filter->range_max;
+			break;
+		default:
+			break;
 		}
 
 		damos_add_filter(scheme, filter);
-- 
2.47.3

[RFC PATCH 7/8] mm/damon/core-kunit: extend damos_commit_filter_for() for wrong input

[SJ Park]

damos_commit_filter_for() supposes damos_commit_filter() to always
succeed with given inputs.  damos_commit_filter() could return an error
for invalid inputs.  Existing callers always pass only valid inputs, but
they may pass invalid inputs in future, for test purposes.  Extend the
function to be able to be used for wrong inputs-caused error testing.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/tests/core-kunit.h | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index a47a5cdf285c8..c9941f3bfb42b 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1127,9 +1127,15 @@ static void damos_test_commit_dests(struct kunit *test)
 }
 
 static void damos_test_commit_filter_for(struct kunit *test,
-		struct damos_filter *dst, struct damos_filter *src)
+		struct damos_filter *dst, struct damos_filter *src,
+		bool expect_fail)
 {
-	damos_commit_filter(dst, src);
+	int err;
+
+	err = damos_commit_filter(dst, src);
+	KUNIT_EXPECT_EQ(test, err != 0, expect_fail);
+	if (expect_fail)
+		return;
 	KUNIT_EXPECT_EQ(test, dst->type, src->type);
 	KUNIT_EXPECT_EQ(test, dst->matching, src->matching);
 	KUNIT_EXPECT_EQ(test, dst->allow, src->allow);
@@ -1168,47 +1174,47 @@ static void damos_test_commit_filter(struct kunit *test)
 			.type = DAMOS_FILTER_TYPE_ANON,
 			.matching = true,
 			.allow = true,
-			});
+			}, false);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_MEMCG,
 			.matching = false,
 			.allow = false,
 			.memcg_id = 123,
-			});
+			}, false);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_YOUNG,
 			.matching = true,
 			.allow = true,
-			});
+			}, false);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_HUGEPAGE_SIZE,
 			.matching = false,
 			.allow = false,
 			.sz_range = {.min = 234, .max = 345},
-			});
+			}, false);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_UNMAPPED,
 			.matching = true,
 			.allow = true,
-			});
+			}, false);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_ADDR,
 			.matching = false,
 			.allow = false,
 			.addr_range = {.start = 456, .end = 567},
-			});
+			}, false);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_TARGET,
 			.matching = true,
 			.allow = true,
 			.target_idx = 6,
-			});
+			}, false);
 }
 
 static void damos_test_help_initailize_scheme(struct damos *scheme)
-- 
2.47.3

[RFC PATCH 8/8] mm/damon/core-kunit: test invalid damos filter commits

[SJ Park]

Add test cases for testing the validation of damos filter arguments in
commit time.

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/tests/core-kunit.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index c9941f3bfb42b..5da84caf4124d 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1195,6 +1195,13 @@ static void damos_test_commit_filter(struct kunit *test)
 			.allow = false,
 			.sz_range = {.min = 234, .max = 345},
 			}, false);
+	damos_test_commit_filter_for(test, &dst,
+			&(struct damos_filter){
+			.type = DAMOS_FILTER_TYPE_HUGEPAGE_SIZE,
+			.matching = false,
+			.allow = false,
+			.sz_range = {.min = 456, .max = 123},
+			}, true);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_UNMAPPED,
@@ -1208,6 +1215,13 @@ static void damos_test_commit_filter(struct kunit *test)
 			.allow = false,
 			.addr_range = {.start = 456, .end = 567},
 			}, false);
+	damos_test_commit_filter_for(test, &dst,
+			&(struct damos_filter){
+			.type = DAMOS_FILTER_TYPE_ADDR,
+			.matching = false,
+			.allow = false,
+			.addr_range = {.start = 567, .end = 456},
+			}, true);
 	damos_test_commit_filter_for(test, &dst,
 			&(struct damos_filter){
 			.type = DAMOS_FILTER_TYPE_TARGET,
-- 
2.47.3