* + mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch added to mm-unstable branch
@ 2022-12-15 21:05 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2022-12-15 21:05 UTC (permalink / raw)
To: mm-commits, songmuchun, catalin.marinas, longman, akpm
The patch titled
Subject: mm/kmemleak: simplify kmemleak_cond_resched() usage
has been added to the -mm mm-unstable branch. Its filename is
mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Waiman Long <longman@redhat.com>
Subject: mm/kmemleak: simplify kmemleak_cond_resched() usage
Date: Thu, 15 Dec 2022 11:02:58 -0500
Patch series "mm/kmemleak: Simplify kmemleak_cond_resched() & fix UAF",
v2.
It was found that a KASAN use-after-free error was reported in
kmemleak_scan(). After further examination, it is believed that even
though a reference is taken from the current object, it does not prevent
the object pointed to by the next pointer from going away after a
cond_resched().
To fix that, additional flags are added to make sure that the current
object won't be removed from the object_list during the duration of
the cond_resched() to ensure the validity of the next pointer.
While making the change, I also simplified the current usage of
kmemleak_cond_resched() to make it easier to understand.
The presence of a pinned argument and the 64k loop count make
kmemleak_cond_resched() a bit more complex to read. The pinned argument
is used only by first kmemleak_scan() loop.
Simplify the usage of kmemleak_cond_resched() by removing the pinned
argument and always do a get_object()/put_object() sequence. In addition,
the 64k loop is removed by using need_resched() to decide if
kmemleak_cond_resched() should be called.
Link: https://lkml.kernel.org/r/20221215160259.261136-1-longman@redhat.com
Link: https://lkml.kernel.org/r/20221215160259.261136-2-longman@redhat.com
Fixes: 6edda04ccc7c ("mm/kmemleak: prevent soft lockup in first object iteration loop of kmemleak_scan()")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/kmemleak.c | 48 ++++++++++++------------------------------------
1 file changed, 12 insertions(+), 36 deletions(-)
--- a/mm/kmemleak.c~mm-kmemleak-simplify-kmemleak_cond_resched-usage
+++ a/mm/kmemleak.c
@@ -1472,22 +1472,17 @@ static void scan_gray_list(void)
/*
* Conditionally call resched() in an object iteration loop while making sure
* that the given object won't go away without RCU read lock by performing a
- * get_object() if !pinned.
- *
- * Return: false if can't do a cond_resched() due to get_object() failure
- * true otherwise
+ * get_object() if necessaary.
*/
-static bool kmemleak_cond_resched(struct kmemleak_object *object, bool pinned)
+static void kmemleak_cond_resched(struct kmemleak_object *object)
{
- if (!pinned && !get_object(object))
- return false;
+ if (!get_object(object))
+ return; /* Try next object */
rcu_read_unlock();
cond_resched();
rcu_read_lock();
- if (!pinned)
- put_object(object);
- return true;
+ put_object(object);
}
/*
@@ -1501,15 +1496,12 @@ static void kmemleak_scan(void)
struct zone *zone;
int __maybe_unused i;
int new_leaks = 0;
- int loop_cnt = 0;
jiffies_last_scan = jiffies;
/* prepare the kmemleak_object's */
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
- bool obj_pinned = false;
-
raw_spin_lock_irq(&object->lock);
#ifdef DEBUG
/*
@@ -1535,19 +1527,13 @@ static void kmemleak_scan(void)
/* reset the reference count (whiten the object) */
object->count = 0;
- if (color_gray(object) && get_object(object)) {
+ if (color_gray(object) && get_object(object))
list_add_tail(&object->gray_list, &gray_list);
- obj_pinned = true;
- }
raw_spin_unlock_irq(&object->lock);
- /*
- * Do a cond_resched() every 64k objects to avoid soft lockup.
- */
- if (!(++loop_cnt & 0xffff) &&
- !kmemleak_cond_resched(object, obj_pinned))
- loop_cnt--; /* Try again on next object */
+ if (need_resched())
+ kmemleak_cond_resched(object);
}
rcu_read_unlock();
@@ -1614,14 +1600,9 @@ static void kmemleak_scan(void)
* scan and color them gray until the next scan.
*/
rcu_read_lock();
- loop_cnt = 0;
list_for_each_entry_rcu(object, &object_list, object_list) {
- /*
- * Do a cond_resched() every 64k objects to avoid soft lockup.
- */
- if (!(++loop_cnt & 0xffff) &&
- !kmemleak_cond_resched(object, false))
- loop_cnt--; /* Try again on next object */
+ if (need_resched())
+ kmemleak_cond_resched(object);
/*
* This is racy but we can save the overhead of lock/unlock
@@ -1656,14 +1637,9 @@ static void kmemleak_scan(void)
* Scanning result reporting.
*/
rcu_read_lock();
- loop_cnt = 0;
list_for_each_entry_rcu(object, &object_list, object_list) {
- /*
- * Do a cond_resched() every 64k objects to avoid soft lockup.
- */
- if (!(++loop_cnt & 0xffff) &&
- !kmemleak_cond_resched(object, false))
- loop_cnt--; /* Try again on next object */
+ if (need_resched())
+ kmemleak_cond_resched(object);
/*
* This is racy but we can save the overhead of lock/unlock
_
Patches currently in -mm which might be from longman@redhat.com are
mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch
mm-kmemleak-fix-uaf-bug-in-kmemleak_scan.patch
^ permalink raw reply [flat|nested] 2+ messages in thread
* + mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch added to mm-unstable branch
@ 2023-01-19 22:17 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2023-01-19 22:17 UTC (permalink / raw)
To: mm-commits, songmuchun, catalin.marinas, longman, akpm
The patch titled
Subject: mm/kmemleak: simplify kmemleak_cond_resched() usage
has been added to the -mm mm-unstable branch. Its filename is
mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Waiman Long <longman@redhat.com>
Subject: mm/kmemleak: simplify kmemleak_cond_resched() usage
Date: Wed, 18 Jan 2023 23:01:10 -0500
Patch series "mm/kmemleak: Simplify kmemleak_cond_resched() & fix UAF", v2.
It was found that a KASAN use-after-free error was reported in the
kmemleak_scan() function. After further examination, it is believe that
even though a reference is taken from the current object, it does not
prevent the object pointed to by the next pointer from going away after a
cond_resched().
To fix that, additional flags are added to make sure that the current
object won't be removed from the object_list during the duration of the
cond_resched() to ensure the validity of the next pointer.
While making the change, I also simplify the current usage of
kmemleak_cond_resched() to make it easier to understand.
This patch (of 2):
The presence of a pinned argument and the 64k loop count make
kmemleak_cond_resched() a bit more complex to read. The pinned argument
is used only by first kmemleak_scan() loop.
Simplify the usage of kmemleak_cond_resched() by removing the pinned
argument and always do a get_object()/put_object() sequence. In addition,
the 64k loop is removed by using need_resched() to decide if
kmemleak_cond_resched() should be called.
Link: https://lkml.kernel.org/r/20230119040111.350923-1-longman@redhat.com
Link: https://lkml.kernel.org/r/20230119040111.350923-2-longman@redhat.com
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
--- a/mm/kmemleak.c~mm-kmemleak-simplify-kmemleak_cond_resched-usage
+++ a/mm/kmemleak.c
@@ -1472,22 +1472,17 @@ static void scan_gray_list(void)
/*
* Conditionally call resched() in an object iteration loop while making sure
* that the given object won't go away without RCU read lock by performing a
- * get_object() if !pinned.
- *
- * Return: false if can't do a cond_resched() due to get_object() failure
- * true otherwise
+ * get_object() if necessaary.
*/
-static bool kmemleak_cond_resched(struct kmemleak_object *object, bool pinned)
+static void kmemleak_cond_resched(struct kmemleak_object *object)
{
- if (!pinned && !get_object(object))
- return false;
+ if (!get_object(object))
+ return; /* Try next object */
rcu_read_unlock();
cond_resched();
rcu_read_lock();
- if (!pinned)
- put_object(object);
- return true;
+ put_object(object);
}
/*
@@ -1501,15 +1496,12 @@ static void kmemleak_scan(void)
struct zone *zone;
int __maybe_unused i;
int new_leaks = 0;
- int loop_cnt = 0;
jiffies_last_scan = jiffies;
/* prepare the kmemleak_object's */
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
- bool obj_pinned = false;
-
raw_spin_lock_irq(&object->lock);
#ifdef DEBUG
/*
@@ -1535,19 +1527,13 @@ static void kmemleak_scan(void)
/* reset the reference count (whiten the object) */
object->count = 0;
- if (color_gray(object) && get_object(object)) {
+ if (color_gray(object) && get_object(object))
list_add_tail(&object->gray_list, &gray_list);
- obj_pinned = true;
- }
raw_spin_unlock_irq(&object->lock);
- /*
- * Do a cond_resched() every 64k objects to avoid soft lockup.
- */
- if (!(++loop_cnt & 0xffff) &&
- !kmemleak_cond_resched(object, obj_pinned))
- loop_cnt--; /* Try again on next object */
+ if (need_resched())
+ kmemleak_cond_resched(object);
}
rcu_read_unlock();
@@ -1614,14 +1600,9 @@ static void kmemleak_scan(void)
* scan and color them gray until the next scan.
*/
rcu_read_lock();
- loop_cnt = 0;
list_for_each_entry_rcu(object, &object_list, object_list) {
- /*
- * Do a cond_resched() every 64k objects to avoid soft lockup.
- */
- if (!(++loop_cnt & 0xffff) &&
- !kmemleak_cond_resched(object, false))
- loop_cnt--; /* Try again on next object */
+ if (need_resched())
+ kmemleak_cond_resched(object);
/*
* This is racy but we can save the overhead of lock/unlock
@@ -1656,14 +1637,9 @@ static void kmemleak_scan(void)
* Scanning result reporting.
*/
rcu_read_lock();
- loop_cnt = 0;
list_for_each_entry_rcu(object, &object_list, object_list) {
- /*
- * Do a cond_resched() every 64k objects to avoid soft lockup.
- */
- if (!(++loop_cnt & 0xffff) &&
- !kmemleak_cond_resched(object, false))
- loop_cnt--; /* Try again on next object */
+ if (need_resched())
+ kmemleak_cond_resched(object);
/*
* This is racy but we can save the overhead of lock/unlock
_
Patches currently in -mm which might be from longman@redhat.com are
mm-kmemleak-simplify-kmemleak_cond_resched-usage.patch
mm-kmemleak-fix-uaf-bug-in-kmemleak_scan.patch
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