Re: [PATCH v1 1/5] misc: fastrpc: Add NULL check to fastrpc_buf_free to prevent crash

[Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>]

On 5/13/25 05:28, Ekansh Gupta wrote:
> The fastrpc_buf_free function currently does not handle the case where
> the input buffer pointer (buf) is NULL. This can lead to a null pointer
> dereference, causing a crash or undefined behavior when the function
> attempts to access members of the buf structure. Add a NULL check to
> ensure safe handling of NULL pointers and prevent potential crashes.
> 
You are mostly defining the code here, but not the root cause of it,
What exactly is the call trace for this crash?

> Fixes: c68cfb718c8f9 ("misc: fastrpc: Add support for context Invoke method")
> Cc: stable@kernel.org
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/misc/fastrpc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 7b7a22c91fe4..ca3721365ddc 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -394,6 +394,9 @@ static int fastrpc_map_lookup(struct fastrpc_user *fl, int fd,
>  
>  static void fastrpc_buf_free(struct fastrpc_buf *buf)
>  {
> +	if (!buf)
> +		return;
> +
Most of the users of the fastrpc_buf_free() already have the null
checks, It will be Interesting to know.

If we decide to make this function to do null null check, then the
existing checks in the caller are redundant.

--srini
>  	dma_free_coherent(buf->dev, buf->size, buf->virt,
>  			  FASTRPC_PHYS(buf->phys));
>  	kfree(buf);