linux-kernel - Re: [PATCH v2] ipr: fix out-of-bounds null overwrite

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Date:	Wed, 6 Jan 2016 11:26:06 -0600
From:	"Matthew R. Ochs" <mrochs@...ux.vnet.ibm.com>
To:	Insu Yun <wuninsu@...il.com>
Cc:	brking@...ibm.com, JBottomley@...n.com, martin.petersen@...cle.com,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	taesoo@...ech.edu, yeongjin.jang@...ech.edu, insu@...ech.edu,
	changwoo@...ech.edu
Subject: Re: [PATCH v2] ipr: fix out-of-bounds null overwrite

On Jan 6, 2016, at 7:53 AM, Insu Yun <wuninsu@...il.com> wrote:
> 
> Return value of snprintf is not bound by size value, 2nd argument.
> (https://www.kernel.org/doc/htmldocs/kernel-api/API-snprintf.html).
> Return value is number of printed chars, can be larger than 2nd argument.
> Therefore, it can write null byte out of bounds ofbuffer.
> Since snprintf puts null, it does not need to put additional null byte.
> 
> Signed-off-by: Insu Yun <wuninsu@...il.com>
> ---
> drivers/scsi/ipr.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
> index 536cd5a..caf63f9 100644
> --- a/drivers/scsi/ipr.c
> +++ b/drivers/scsi/ipr.c
> @@ -4003,13 +4003,12 @@ static ssize_t ipr_store_update_fw(struct device *dev,
> 	struct ipr_sglist *sglist;
> 	char fname[100];
> 	char *src;
> -	int len, result, dnld_size;
> +	int result, dnld_size;
> 
> 	if (!capable(CAP_SYS_ADMIN))
> 		return -EACCES;
> 
> -	len = snprintf(fname, 99, "%s", buf);
> -	fname[len-1] = '\0';
> +	snprintf(fname, 99, "%s", buf);

Changing the 99 to sizeof(fname) as part of this change would also
make for cleaner code in my opinion. Will leave it up to you if you'd
like to do a v3.

Reviewed-by: Matthew R. Ochs <mrochs@...ux.vnet.ibm.com> 
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