linux-kernel - Re: [PATCH v2] misc: fastrpc: Fix double free of 'buf' in error path

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Date:   Mon, 12 Jun 2023 11:57:28 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Sukrut Bellary <sukrut.bellary@...ux.com>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Carpenter <dan.carpenter@...aro.org>,
        Abel Vesa <abel.vesa@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2] misc: fastrpc: Fix double free of 'buf' in error path



On 02/06/2023 12:36, Sukrut Bellary wrote:
> smatch warning:
> drivers/misc/fastrpc.c:1926 fastrpc_req_mmap() error: double free of 'buf'
> 
> In fastrpc_req_mmap() error path, the fastrpc buffer is freed in
> fastrpc_req_munmap_impl() if unmap is successful.
> 
> But in the end, there is an unconditional call to fastrpc_buf_free().
> So the above case triggers the double free of fastrpc buf.
> 
> Fixes: 72fa6f7820c4 ("misc: fastrpc: Rework fastrpc_req_munmap")
> Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>
> Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>
> Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Not sure how was this reviewed-by picked up on this patch.

Suggested-by will be a right choice here.

Will manually edit before applying it.

--srini

> Signed-off-by: Sukrut Bellary <sukrut.bellary@...ux.com>
> ---
> This is based on static analysis. Compilation tested.
> ---
> Changes in v2:
> - Fixed the commit message.
> - Addressed the review comment about deleting buf from the list
>    before freeing.
> - Link to v1: https://lore.kernel.org/all/20230518100829.515143-1-sukrut.bellary@linux.com/
> ---
>   drivers/misc/fastrpc.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index f48466960f1b..b3b520fcfb75 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1882,7 +1882,8 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
>   				      &args[0]);
>   	if (err) {
>   		dev_err(dev, "mmap error (len 0x%08llx)\n", buf->size);
> -		goto err_invoke;
> +		fastrpc_buf_free(buf);
> +		return err;
>   	}
>   
>   	/* update the buffer to be able to deallocate the memory on the DSP */
> @@ -1922,8 +1923,6 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
>   
>   err_assign:
>   	fastrpc_req_munmap_impl(fl, buf);
> -err_invoke:
> -	fastrpc_buf_free(buf);
>   
>   	return err;
>   }