linux-kernel - RE: [PATCH, net-next] net: ethernet: freescale: fix false-positive string overflow warning

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Message-ID: <AM4PR0401MB22605C57F8899AC2416BEF57FF6D0@AM4PR0401MB2260.eurprd04.prod.outlook.com>
Date:   Tue, 29 May 2018 01:10:30 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>
CC:     Fabio Estevam <fabio.estevam@....com>,
        Andrew Lunn <andrew@...n.ch>,
        Troy Kisky <troy.kisky@...ndarydevices.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH, net-next] net: ethernet: freescale: fix false-positive
 string overflow warning

From: Arnd Bergmann <arnd@...db.de> Sent: 2018年5月28日 23:50
> While compile-testing on arm64 with gcc-8.1, I ran into a build diagnostic:
> 
> drivers/net/ethernet/freescale/fec_main.c: In function 'fec_probe':
> drivers/net/ethernet/freescale/fec_main.c:3517:25: error: '%d' directive
> writing between 1 and 10 bytes into a region of size 5
> [-Werror=format-overflow=]
>    sprintf(irq_name, "int%d", i);
>                          ^~
> drivers/net/ethernet/freescale/fec_main.c:3517:21: note: directive
> argument in the range [0, 2147483646]
>    sprintf(irq_name, "int%d", i);
>                      ^~~~~~~
> drivers/net/ethernet/freescale/fec_main.c:3517:3: note: 'sprintf' output
> between 5 and 14 bytes into a destination of size 8
>    sprintf(irq_name, "int%d", i);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> It appears this has never shown on ppc32 or arm32 for an unknown
> reason, but now gcc fails to identify that the 'irq_cnt' loop index has an
> upper bound of 3, and instead uses a bogus range.
> 
> To work around the warning, this changes the sprintf to snprintf with the
> correct buffer length.
> 
> Fixes: 78cc6e7ef957 ("net: ethernet: freescale: Allow FEC with
> COMPILE_TEST")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Fugang Duan <fugang.duan@....com>

> ---
>  drivers/net/ethernet/freescale/fec_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> b/drivers/net/ethernet/freescale/fec_main.c
> index ab7521c04eb2..c729665107f5 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -3514,7 +3514,7 @@ fec_probe(struct platform_device *pdev)
>  		goto failed_init;
> 
>  	for (i = 0; i < irq_cnt; i++) {
> -		sprintf(irq_name, "int%d", i);
> +		snprintf(irq_name, sizeof(irq_name), "int%d", i);
>  		irq = platform_get_irq_byname(pdev, irq_name);
>  		if (irq < 0)
>  			irq = platform_get_irq(pdev, i);
> --
> 2.9.0