linux-kernel - Re: [PATCH] misc: fastrpc: fix potential fastrpc_invoke

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Date:   Mon, 11 May 2020 18:18:10 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc:     gregkh@...uxfoundation.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, arnd@...db.de,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] misc: fastrpc: fix potential fastrpc_invoke_ctx leak

On Mon 11 May 09:29 PDT 2020, Srinivas Kandagatla wrote:

> fastrpc_invoke_ctx can have refcount of 2 in error path where
> rpmsg_send() fails to send invoke message. decrement the refcount
> properly in the error path to fix this leak.
> 
> This also fixes below static checker warning:
> 
> drivers/misc/fastrpc.c:990 fastrpc_internal_invoke()
> warn: 'ctx->refcount.refcount.ref.counter' not decremented on lines: 990.
> 
> Fixes: c68cfb718c8f ("misc: fastrpc: Add support for context")
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> ---
>  drivers/misc/fastrpc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 9065d3e71ff7..07065728e39f 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -949,8 +949,10 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
>  	dma_wmb();
>  	/* Send invoke buffer to remote dsp */
>  	err = fastrpc_invoke_send(fl->sctx, ctx, kernel, handle);
> -	if (err)
> +	if (err) {
> +		fastrpc_context_put(ctx);

So we refcount ctx once for the invoke function and once between send
and callback. And this fastrpc_context_put() would counter the fact that
rpmsg_send() failed, so we will not get the "remote's" put().

I think that if you moved this call inside fastrpc_invoke_send() it's
relationship to the failing rpmsg_send() would be obvious.

Regards,
Bjorn

>  		goto bail;
> +	}
>  
>  	if (kernel) {
>  		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
> -- 
> 2.21.0
>