- Enforce alloc->mutex in binder_alloc_mmap_handler when add the entry to
list.
- Assign the freed pages/page_ptr to NULL to catch possible use after free
with NULL pointer access.
Fixes: 19c987241ca1 ("binder: separate out binder_alloc functions")
Fixes: f2517eb76f1f ("android: binder: Add global lru shrinker to binder")
CC: Todd Kjos <[email protected]>
CC: Sherry Yang <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Kassey Li <[email protected]>
---
V1 -> V2: Add Fixes info.
V2 -> V3: Add this history.
---
drivers/android/binder_alloc.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index e3db8297095a..c7d126e04343 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -775,6 +775,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
}
buffer->user_data = alloc->buffer;
+ mutex_lock(&alloc->mutex);
list_add(&buffer->entry, &alloc->buffers);
buffer->free = 1;
binder_insert_free_buffer(alloc, buffer);
@@ -782,7 +783,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
/* Signal binder_alloc is fully initialized */
binder_alloc_set_vma(alloc, vma);
-
+ mutex_unlock(&alloc->mutex);
return 0;
err_alloc_buf_struct_failed:
@@ -856,9 +857,11 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
__func__, alloc->pid, i, page_addr,
on_lru ? "on lru" : "active");
__free_page(alloc->pages[i].page_ptr);
+ alloc->pages[i].page_ptr = NULL;
page_count++;
}
kfree(alloc->pages);
+ alloc->pages = NULL;
}
mutex_unlock(&alloc->mutex);
if (alloc->mm)
--
2.25.1
On Sat, Oct 07, 2023 at 08:28:13PM +0800, Kassey Li wrote:
> - Enforce alloc->mutex in binder_alloc_mmap_handler when add the entry to
> list.
>
> - Assign the freed pages/page_ptr to NULL to catch possible use after free
> with NULL pointer access.
>
> Fixes: 19c987241ca1 ("binder: separate out binder_alloc functions")
> Fixes: f2517eb76f1f ("android: binder: Add global lru shrinker to binder")
> CC: Todd Kjos <[email protected]>
> CC: Sherry Yang <[email protected]>
> Link: https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Kassey Li <[email protected]>
> ---
> V1 -> V2: Add Fixes info.
> V2 -> V3: Add this history.
> ---
> drivers/android/binder_alloc.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> index e3db8297095a..c7d126e04343 100644
> --- a/drivers/android/binder_alloc.c
> +++ b/drivers/android/binder_alloc.c
> @@ -775,6 +775,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
> }
>
> buffer->user_data = alloc->buffer;
> + mutex_lock(&alloc->mutex);
At this stage we are already holding the mm->mmap_lock. If you take the
alloc->mutex here you will deadlock. You should see this warning with
lockdep enabled. Also, you don't need the lock here...
> list_add(&buffer->entry, &alloc->buffers);
> buffer->free = 1;
> binder_insert_free_buffer(alloc, buffer);
> @@ -782,7 +783,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
>
> /* Signal binder_alloc is fully initialized */
> binder_alloc_set_vma(alloc, vma);
This barrier will set the alloc->vma pointer. Once set, it signals that
the alloc-> space has been initialized and it is safe to access.
> -
> + mutex_unlock(&alloc->mutex);
> return 0;
>
> err_alloc_buf_struct_failed:
> @@ -856,9 +857,11 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
> __func__, alloc->pid, i, page_addr,
> on_lru ? "on lru" : "active");
> __free_page(alloc->pages[i].page_ptr);
> + alloc->pages[i].page_ptr = NULL;
> page_count++;
> }
> kfree(alloc->pages);
> + alloc->pages = NULL;
The process is dying and there aren't any more references to it. It is
pointless to mark the pages NULL. No one is or will use them after.
> }
> mutex_unlock(&alloc->mutex);
> if (alloc->mm)
> --
> 2.25.1
>
I see that you reported a crash on the previous thread here:
https://lore.kernel.org/all/[email protected]/
...unfortunately, it doesn't seem to me like setting alloc->pages = NULL
would help fix your issue.
I do agree this sounds like a use-after-free though. Are you able to
reproduce the issue with KASAN enabled? This should tell us where the
actual problem is.
--
Carlos Llamas
On 2023/10/8 7:16, Carlos Llamas wrote:
> On Sat, Oct 07, 2023 at 08:28:13PM +0800, Kassey Li wrote:
>> - Enforce alloc->mutex in binder_alloc_mmap_handler when add the entry to
>> list.
>>
>> - Assign the freed pages/page_ptr to NULL to catch possible use after free
>> with NULL pointer access.
>>
>> Fixes: 19c987241ca1 ("binder: separate out binder_alloc functions")
>> Fixes: f2517eb76f1f ("android: binder: Add global lru shrinker to binder")
>> CC: Todd Kjos <[email protected]>
>> CC: Sherry Yang <[email protected]>
>> Link: https://lore.kernel.org/all/[email protected]/
>> Signed-off-by: Kassey Li <[email protected]>
>> ---
>> V1 -> V2: Add Fixes info.
>> V2 -> V3: Add this history.
>> ---
>> drivers/android/binder_alloc.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
>> index e3db8297095a..c7d126e04343 100644
>> --- a/drivers/android/binder_alloc.c
>> +++ b/drivers/android/binder_alloc.c
>> @@ -775,6 +775,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
>> }
>>
>> buffer->user_data = alloc->buffer;
>> + mutex_lock(&alloc->mutex);
>
> At this stage we are already holding the mm->mmap_lock. If you take the
> alloc->mutex here you will deadlock. You should see this warning with
> lockdep enabled. Also, you don't need the lock here...
lockdep did not warn, but i agree with you, i did not aware the
mm->mmap_lock. thanks for the remind.
>
>> list_add(&buffer->entry, &alloc->buffers);
>> buffer->free = 1;
>> binder_insert_free_buffer(alloc, buffer);
>> @@ -782,7 +783,7 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
>>
>> /* Signal binder_alloc is fully initialized */
>> binder_alloc_set_vma(alloc, vma);
>
> This barrier will set the alloc->vma pointer. Once set, it signals that
> the alloc-> space has been initialized and it is safe to access.
>
>> -
>> + mutex_unlock(&alloc->mutex);
>> return 0;
>>
>> err_alloc_buf_struct_failed:
>> @@ -856,9 +857,11 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc)
>> __func__, alloc->pid, i, page_addr,
>> on_lru ? "on lru" : "active");
>> __free_page(alloc->pages[i].page_ptr);
>> + alloc->pages[i].page_ptr = NULL;
>> page_count++;
>> }
>> kfree(alloc->pages);
>> + alloc->pages = NULL;
>
> The process is dying and there aren't any more references to it. It is
> pointless to mark the pages NULL. No one is or will use them after.
looks correct.
>
>> }
>> mutex_unlock(&alloc->mutex);
>> if (alloc->mm)
>> --
>> 2.25.1
>>
>
> I see that you reported a crash on the previous thread here:
> https://lore.kernel.org/all/[email protected]/
> ...unfortunately, it doesn't seem to me like setting alloc->pages = NULL
> would help fix your issue.
>
> I do agree this sounds like a use-after-free though. Are you able to
> reproduce the issue with KASAN enabled? This should tell us where the
> actual problem is.
kasan is trying but not reproduced yet, we will chasing with this
test enable kasan.
>
> --
> Carlos Llamas