Re: [PATCH v2] binder: add mutex_lock for mmap and NULL when free

[Greg KH]

On Sat, Oct 07, 2023 at 07:45:24PM +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")
> Signed-off-by: Kassey Li <quic_yingangl@xxxxxxxxxxx>
> ---
>  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
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
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- You have marked a patch with a "Fixes:" tag for a commit that is in an
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  Documentation/process/stable-kernel-rules.rst file for how to resolve
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If you wish to discuss this problem further, or you have questions about
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Greg will reply once he has dug out from the pending patches received
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thanks,

greg k-h's patch email bot