[PATCH v1 4/5] misc: fastrpc: Remove buffer from list prior to unmap operation

[Dmitry Baryshkov]

On Tue, May 13, 2025 at 09:58:24AM +0530, Ekansh Gupta wrote:
> fastrpc_req_munmap_impl() is called to unmap any buffer. The buffer is
> getting removed from the list after it is unmapped from DSP. This can
> create potential race conditions if any other thread removes the entry
> from list while unmap operation is ongoing. Remove the entry before
> calling unmap operation.
> 
> Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
> Cc: stable at kernel.org
> Signed-off-by: Ekansh Gupta <ekansh.gupta at oss.qualcomm.com>
> ---
>  drivers/misc/fastrpc.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index b629e24f00bc..d54368bf8c5c 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1868,9 +1868,6 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user *fl, struct fastrpc_buf *
>  				      &args[0]);
>  	if (!err) {
>  		dev_dbg(dev, "unmmap\tpt 0x%09lx OK\n", buf->raddr);
> -		spin_lock(&fl->lock);
> -		list_del(&buf->node);
> -		spin_unlock(&fl->lock);
>  		fastrpc_buf_free(buf);
>  	} else {
>  		dev_err(dev, "unmmap\tpt 0x%09lx ERROR\n", buf->raddr);
> @@ -1884,13 +1881,15 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
>  	struct fastrpc_buf *buf = NULL, *iter, *b;
>  	struct fastrpc_req_munmap req;
>  	struct device *dev = fl->sctx->dev;
> +	int err;
>  
>  	if (copy_from_user(&req, argp, sizeof(req)))
>  		return -EFAULT;
>  
>  	spin_lock(&fl->lock);
>  	list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
> -		if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
> +		if (iter->raddr == req.vaddrout && iter->size == req.size) {

Cosmetics, please drop.

> +			list_del(&iter->node);
>  			buf = iter;
>  			break;
>  		}
> @@ -1903,7 +1902,14 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
>  		return -EINVAL;
>  	}
>  
> -	return fastrpc_req_munmap_impl(fl, buf);
> +	err = fastrpc_req_munmap_impl(fl, buf);
> +	if (err) {
> +		spin_lock(&fl->lock);
> +		list_add_tail(&buf->node, &fl->mmaps);
> +		spin_unlock(&fl->lock);
> +	}
> +
> +	return err;
>  }
>  
>  static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
> @@ -1997,14 +2003,23 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
>  
>  	if (copy_to_user((void __user *)argp, &req, sizeof(req))) {
>  		err = -EFAULT;
> -		goto err_assign;
> +		goto err_copy;
>  	}
>  
>  	dev_dbg(dev, "mmap\t\tpt 0x%09lx OK [len 0x%08llx]\n",
>  		buf->raddr, buf->size);
>  
>  	return 0;
> -

Please keep the empty line here, it improves readability.

> +err_copy:
> +	if (req.flags == ADSP_MMAP_REMOTE_HEAP_ADDR) {
> +		spin_lock_irqsave(&fl->cctx->lock, flags);
> +		list_del(&buf->node);
> +		spin_unlock_irqrestore(&fl->cctx->lock, flags);
> +	} else {
> +		spin_lock(&fl->lock);
> +		list_del(&buf->node);
> +		spin_unlock(&fl->lock);
> +	}

Can we store the spinlock pointer in the struct fastrpc_buf instead?

>  err_assign:
>  	fastrpc_req_munmap_impl(fl, buf);
>  
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry