* [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount
@ 2020-03-30 21:30 Qian Cai
2020-04-06 13:31 ` Qian Cai
2020-04-08 12:20 ` [tip: locking/urgent] locking/percpu-rwsem: Fix " tip-bot2 for Qian Cai
0 siblings, 2 replies; 4+ messages in thread
From: Qian Cai @ 2020-03-30 21:30 UTC (permalink / raw)
To: peterz, mingo; +Cc: will, dbueso, juri.lelli, longman, linux-kernel, Qian Cai
The commit 7f26482a872c ("locking/percpu-rwsem: Remove the embedded
rwsem") introduced some task_struct memory leaks due to messing up with
a task_struct refcount. At the beginning of
percpu_rwsem_wake_function(), it calls get_task_struct(), but if the
trylock failed, it will remain in the waitqueue. However, it will run
percpu_rwsem_wake_function() again with get_task_struct() to increase
the refcount but then only call put_task_struct() once the trylock
succeeded.
Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against
when percpu_rwsem_wait() observing !private, terminating the wait and
doing a quick exit() while percpu_rwsem_wake_function() then doing
wake_up_process(p) as a use-after-free.
Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Qian Cai <cai@lca.pw>
---
kernel/locking/percpu-rwsem.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index a008a1ba21a7..8bbafe3e5203 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -118,14 +118,15 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
unsigned int mode, int wake_flags,
void *key)
{
- struct task_struct *p = get_task_struct(wq_entry->private);
bool reader = wq_entry->flags & WQ_FLAG_CUSTOM;
struct percpu_rw_semaphore *sem = key;
+ struct task_struct *p;
/* concurrent against percpu_down_write(), can get stolen */
if (!__percpu_rwsem_trylock(sem, reader))
return 1;
+ p = get_task_struct(wq_entry->private);
list_del_init(&wq_entry->entry);
smp_store_release(&wq_entry->private, NULL);
--
2.21.0 (Apple Git-122.2)
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount
2020-03-30 21:30 [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount Qian Cai
@ 2020-04-06 13:31 ` Qian Cai
2020-04-06 14:09 ` Peter Zijlstra
2020-04-08 12:20 ` [tip: locking/urgent] locking/percpu-rwsem: Fix " tip-bot2 for Qian Cai
1 sibling, 1 reply; 4+ messages in thread
From: Qian Cai @ 2020-04-06 13:31 UTC (permalink / raw)
To: Peter Zijlstra, Ingo Molnar
Cc: Will Deacon, dbueso, juri.lelli, Waiman Long, linux-kernel
> On Mar 30, 2020, at 5:30 PM, Qian Cai <cai@lca.pw> wrote:
>
> The commit 7f26482a872c ("locking/percpu-rwsem: Remove the embedded
> rwsem") introduced some task_struct memory leaks due to messing up with
> a task_struct refcount. At the beginning of
> percpu_rwsem_wake_function(), it calls get_task_struct(), but if the
> trylock failed, it will remain in the waitqueue. However, it will run
> percpu_rwsem_wake_function() again with get_task_struct() to increase
> the refcount but then only call put_task_struct() once the trylock
> succeeded.
>
> Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against
> when percpu_rwsem_wait() observing !private, terminating the wait and
> doing a quick exit() while percpu_rwsem_wake_function() then doing
> wake_up_process(p) as a use-after-free.
>
> Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
Peter, Ingo, can you take a look at this patch when you have a chance?
For some reasons Ingo had decided to send a pull request which is now merged
even though I had informed the commit was broken a few days earlier, it makes no
sense to leave known memory leaks in mainline like this.
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> kernel/locking/percpu-rwsem.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
> index a008a1ba21a7..8bbafe3e5203 100644
> --- a/kernel/locking/percpu-rwsem.c
> +++ b/kernel/locking/percpu-rwsem.c
> @@ -118,14 +118,15 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
> unsigned int mode, int wake_flags,
> void *key)
> {
> - struct task_struct *p = get_task_struct(wq_entry->private);
> bool reader = wq_entry->flags & WQ_FLAG_CUSTOM;
> struct percpu_rw_semaphore *sem = key;
> + struct task_struct *p;
>
> /* concurrent against percpu_down_write(), can get stolen */
> if (!__percpu_rwsem_trylock(sem, reader))
> return 1;
>
> + p = get_task_struct(wq_entry->private);
> list_del_init(&wq_entry->entry);
> smp_store_release(&wq_entry->private, NULL);
>
> --
> 2.21.0 (Apple Git-122.2)
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount
2020-04-06 13:31 ` Qian Cai
@ 2020-04-06 14:09 ` Peter Zijlstra
0 siblings, 0 replies; 4+ messages in thread
From: Peter Zijlstra @ 2020-04-06 14:09 UTC (permalink / raw)
To: Qian Cai
Cc: Ingo Molnar, Will Deacon, dbueso, juri.lelli, Waiman Long, linux-kernel
On Mon, Apr 06, 2020 at 09:31:18AM -0400, Qian Cai wrote:
>
>
> > On Mar 30, 2020, at 5:30 PM, Qian Cai <cai@lca.pw> wrote:
> >
> > The commit 7f26482a872c ("locking/percpu-rwsem: Remove the embedded
> > rwsem") introduced some task_struct memory leaks due to messing up with
> > a task_struct refcount. At the beginning of
> > percpu_rwsem_wake_function(), it calls get_task_struct(), but if the
> > trylock failed, it will remain in the waitqueue. However, it will run
> > percpu_rwsem_wake_function() again with get_task_struct() to increase
> > the refcount but then only call put_task_struct() once the trylock
> > succeeded.
> >
> > Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against
> > when percpu_rwsem_wait() observing !private, terminating the wait and
> > doing a quick exit() while percpu_rwsem_wake_function() then doing
> > wake_up_process(p) as a use-after-free.
> >
> > Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
>
> Peter, Ingo, can you take a look at this patch when you have a chance?
I have it queued for urgent, should probably hit tip soon.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip: locking/urgent] locking/percpu-rwsem: Fix a task_struct refcount
2020-03-30 21:30 [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount Qian Cai
2020-04-06 13:31 ` Qian Cai
@ 2020-04-08 12:20 ` tip-bot2 for Qian Cai
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot2 for Qian Cai @ 2020-04-08 12:20 UTC (permalink / raw)
To: linux-tip-commits; +Cc: Peter Zijlstra, Qian Cai, Ingo Molnar, x86, LKML
The following commit has been merged into the locking/urgent branch of tip:
Commit-ID: d22cc7f67d55ebf2d5be865453971c783e9fb21a
Gitweb: https://git.kernel.org/tip/d22cc7f67d55ebf2d5be865453971c783e9fb21a
Author: Qian Cai <cai@lca.pw>
AuthorDate: Mon, 30 Mar 2020 17:30:02 -04:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 08 Apr 2020 12:05:06 +02:00
locking/percpu-rwsem: Fix a task_struct refcount
The following commit:
7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
introduced task_struct memory leaks due to messing up the task_struct
refcount.
At the beginning of percpu_rwsem_wake_function(), it calls get_task_struct(),
but if the trylock failed, it will remain in the waitqueue. However, it
will run percpu_rwsem_wake_function() again with get_task_struct() to
increase the refcount but then only call put_task_struct() once the trylock
succeeded.
Fix it by adjusting percpu_rwsem_wake_function() a bit to guard against
when percpu_rwsem_wait() observing !private, terminating the wait and
doing a quick exit() while percpu_rwsem_wake_function() then doing
wake_up_process(p) as a use-after-free.
Fixes: 7f26482a872c ("locking/percpu-rwsem: Remove the embedded rwsem")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200330213002.2374-1-cai@lca.pw
---
kernel/locking/percpu-rwsem.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index a008a1b..8bbafe3 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -118,14 +118,15 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
unsigned int mode, int wake_flags,
void *key)
{
- struct task_struct *p = get_task_struct(wq_entry->private);
bool reader = wq_entry->flags & WQ_FLAG_CUSTOM;
struct percpu_rw_semaphore *sem = key;
+ struct task_struct *p;
/* concurrent against percpu_down_write(), can get stolen */
if (!__percpu_rwsem_trylock(sem, reader))
return 1;
+ p = get_task_struct(wq_entry->private);
list_del_init(&wq_entry->entry);
smp_store_release(&wq_entry->private, NULL);
^ permalink raw reply related [flat|nested] 4+ messages in thread
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2020-03-30 21:30 [PATCH -next v2] locking/percpu-rwsem: fix a task_struct refcount Qian Cai
2020-04-06 13:31 ` Qian Cai
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2020-04-08 12:20 ` [tip: locking/urgent] locking/percpu-rwsem: Fix " tip-bot2 for Qian Cai
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