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mm/kmemleak: simplify kmemleak_cond_resched() usage 

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>
This commit is contained in:
Waiman Long 2023-01-18 23:01:10 -05:00 committed by Andrew Morton
parent 4cf1fe34fd
commit 6061e74082
1 changed files with 12 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
mm/kmemleak.c
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@ -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