linux-kernel - Re: [RESEND] edac: replace sprintf() by scnprintf()

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Date:   Mon, 12 Jul 2021 13:09:45 +0100
From:   Salah Triki <salah.triki@...il.com>
To:     Joe Perches <joe@...ches.com>
Cc:     bp@...en8.de, mchehab@...nel.org, tony.luck@...el.com,
        james.morse@....com, rric@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND] edac: replace sprintf() by scnprintf()

On Sat, Jul 10, 2021 at 09:58:46AM -0700, Joe Perches wrote:
> On Sat, 2021-07-10 at 17:35 +0100, Salah Triki wrote:
> > Replace sprintf() by scnprintf() in order to avoid buffer overflows.
> 
> While of course safe, this is not strictly necessary as the
> maximum length of any edac_layer_name is 8 bytes.
> 
> drivers/edac/edac_mc.c:const char *edac_layer_name[] = {
> drivers/edac/edac_mc.c- [EDAC_MC_LAYER_BRANCH] = "branch",
> drivers/edac/edac_mc.c- [EDAC_MC_LAYER_CHANNEL] = "channel",
> drivers/edac/edac_mc.c- [EDAC_MC_LAYER_SLOT] = "slot",
> drivers/edac/edac_mc.c- [EDAC_MC_LAYER_CHIP_SELECT] = "csrow",
> drivers/edac/edac_mc.c- [EDAC_MC_LAYER_ALL_MEM] = "memory",
> drivers/edac/edac_mc.c-};
> 
> And name is:
> 
> 		char name[80];
> 
> I suppose name[80] could be changed to name[32] or so
> at the same time to reduce stack usage.
> 
> Maybe name should be moved into the loop too.
> 
> ---
>  drivers/edac/debugfs.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/edac/debugfs.c b/drivers/edac/debugfs.c
> index 4804332d99465..a41071f2ad428 100644
> --- a/drivers/edac/debugfs.c
> +++ b/drivers/edac/debugfs.c
> @@ -55,14 +55,15 @@ void edac_debugfs_exit(void)
>  void edac_create_debugfs_nodes(struct mem_ctl_info *mci)
>  {
>  	struct dentry *parent;
> -	char name[80];
>  	int i;
>  
>  	parent = debugfs_create_dir(mci->dev.kobj.name, edac_debugfs);
>  
>  	for (i = 0; i < mci->n_layers; i++) {
> -		sprintf(name, "fake_inject_%s",
> -			     edac_layer_name[mci->layers[i].type]);
> +		char name[32];
> +
> +		scnprintf(name, sizeof(name), "fake_inject_%s",
> +			  edac_layer_name[mci->layers[i].type]);
>  		debugfs_create_u8(name, S_IRUGO | S_IWUSR, parent,
>  				  &mci->fake_inject_layer[i]);
>  	}
> 
> 

I think name should be [20] since len("fake_inject_") is 12 and maximum 
length of any edac_layer_name is 7 bytes. In addition, for moving the
declaration of name inside the loop we need to compile the source in 
C99 mode.

Thanx