linux-kernel - Re: [PATCH] scsi: 3w-sas: Fix unterminated strncpy

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Message-Id: <1564498597.4300.10.camel@linux.ibm.com>
Date:   Tue, 30 Jul 2019 07:56:37 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Chuhong Yuan <hslester96@...il.com>
Cc:     Adam Radford <aradford@...il.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: 3w-sas: Fix unterminated strncpy

On Tue, 2019-07-30 at 16:40 +0800, Chuhong Yuan wrote:
> strncpy(dest, src, strlen(src)) leads to unterminated
> dest, which is dangerous.

I don't buy that.  The structure is only used for the
TW_IOCTL_GET_COMPATIBILITY_INFO ioctl and all the fields for that are
fixed width and are copied over as such.

> Here driver_version's len is 32 and TW_DRIVER_VERSION
> is shorter than 32.
> Therefore strcpy is OK.

The best practice for copying a string to a fixed width destination
that does get printed within the kernel would be what the 3w-9xxx.c
does

	strlcpy(tw_dev->tw_compat_info.driver_version, TW_DRIVER_VERSION,
		sizeof(tw_dev->tw_compat_info.driver_version));

But as I said, it doesn't really matter for a fixed width field that's
never printed within the kernel.

James