linux-kernel - Re: [PATCH] misc: fastrpc: fix an incorrect NULL check on list iterator

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Message-ID: <20220328170001.GA3040725@trex>
Date:   Mon, 28 Mar 2022 19:00:01 +0200
From:   "Jorge Ramirez-Ortiz, Gmail" <jorge.ramirez.ortiz@...il.com>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     srinivas.kandagatla@...aro.org, amahesh@....qualcomm.com,
        arnd@...db.de, gregkh@...uxfoundation.org,
        jorge.ramirez-ortiz@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] misc: fastrpc: fix an incorrect NULL check on list
 iterator

On 27/03/22, Xiaomeng Tong wrote:
> The bug is here:
> 	if (!buf) {
> 
> The list iterator value 'buf' will *always* be set and non-NULL
> by list_for_each_entry(), so it is incorrect to assume that the
> iterator value will be NULL if the list is empty (in this case, the
> check 'if (!buf) {' will always be false and never exit expectly).

yes.

> 
> To fix the bug, use a new variable 'iter' as the list iterator,
> while use the original variable 'buf' as a dedicated pointer to
> point to the found element.

LGTM

> 
> Cc: stable@...r.kernel.org
> Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> ---
>  drivers/misc/fastrpc.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index aa1682b94a23..45aaf54a7560 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1353,17 +1353,18 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user *fl,
>  				   struct fastrpc_req_munmap *req)
>  {
>  	struct fastrpc_invoke_args args[1] = { [0] = { 0 } };
> -	struct fastrpc_buf *buf, *b;
> +	struct fastrpc_buf *buf = NULL, *iter, *b;
>  	struct fastrpc_munmap_req_msg req_msg;
>  	struct device *dev = fl->sctx->dev;
>  	int err;
>  	u32 sc;
>  
>  	spin_lock(&fl->lock);
> -	list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
> -		if ((buf->raddr == req->vaddrout) && (buf->size == req->size))
> +	list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
> +		if ((iter->raddr == req->vaddrout) && (iter->size == req->size)) {
> +			buf = iter;
>  			break;
> -		buf = NULL;
> +		}
>  	}
>  	spin_unlock(&fl->lock);
>  
> -- 
> 2.17.1
>