linux-kernel - Re: [PATCH] RDMA/ocrdma: Fix an off-by-one issue in 'ocrdma_add

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Message-ID: <20200416130847.GP1163@kadam>
Date:   Thu, 16 Apr 2020 16:08:47 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        selvin.xavier@...adcom.com, devesh.sharma@...adcom.com,
        dledford@...hat.com, leon@...nel.org, colin.king@...onical.com,
        roland@...estorage.com, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] RDMA/ocrdma: Fix an off-by-one issue in 'ocrdma_add_stat'

On Tue, Apr 14, 2020 at 03:34:41PM -0300, Jason Gunthorpe wrote:
> The memcpy is still kind of silly right? What about this:
> 
> static int ocrdma_add_stat(char *start, char *pcur, char *name, u64 count)
> {
> 	size_t len = (start + OCRDMA_MAX_DBGFS_MEM) - pcur;
> 	int cpy_len;
> 
> 	cpy_len = snprintf(pcur, len, "%s: %llu\n", name, count);
> 	if (cpy_len >= len || cpy_len < 0) {

The kernel version of snprintf() doesn't and will never return
negatives.  It would cause a huge security headache if it started
returning negatives.

> 		pr_err("%s: No space in stats buff\n", __func__);
> 		return 0;
> 	}

regards,
dan carpenter