Date: Fri, 23 Feb 2018 22:37:19 +0100 From: Ben RUBSON <ben.rubson@gmail.com> To: Freebsd fs <freebsd-fs@freebsd.org>, FreeBSD-scsi <freebsd-scsi@freebsd.org> Subject: Re: smartmontools and kern.securelevel Message-ID: <A9786FFC-5A0B-42F3-B87B-34D841AE18BF@gmail.com> In-Reply-To: <EA852D1E-6F15-4D3C-9DFB-D5D6F2291E5F@samsco.org> References: <0985ABD3-D141-4EE2-B1B3-3016B16E2B68@gmail.com> <CANCZdfo4PZv7ueCZUZ_bnPu26mL12HAUzfoszhXeDkrTShV6zA@mail.gmail.com> <4C1D44AF-8247-4601-A39C-A8C0A5C8CBD8@gmail.com> <EA852D1E-6F15-4D3C-9DFB-D5D6F2291E5F@samsco.org>
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>> On Feb 23, 2018, at 9:46 AM, Ben RUBSON <ben.rubson@gmail.com> wrote: >> >> On 23 Feb 2018, Warner Losh wrote: >> >>> On Fri, Feb 23, 2018 at 8:20 AM, Ben RUBSON <ben.rubson@gmail.com> wrote: >>> >>>> Hi, >>>> >>>> I run smartmontools on my storage servers, to launch periodic disk >>>> tests and alert on disk errors. >>>> >>>> Unfortunately, if we set sysctl kern.securelevel >=2, smartmontools >>>> does not work anymore. >>>> Certainly because it needs to write directly to raw devices. >>>> (details of the levels, -1 to 3, in security(7)) >>>> >>>> Any workaround to this ? >>>> >>>> Perhaps we could think about allowing SMART commands to be written to >>>> disks when sysctl kern.securelevel >=2 ? >>>> (I assume smartmontools writes SMART commands) >>> >>> Sending raw disks commands is inherently insecure. It's hard to create >>> a list of those commands that are OK because of the complexity and >>> diversity of the needed functionality. That complexity also makes it >>> hard to put the commands into a series of ioctls which could be made >>> more secure. >> >> Thank you for your feedback Warner. >> >> Can't all SMART commands be easily identified among the others ? (when a >> command arrives, does kernel sees it is SMART flagged ?) >> Perhaps you assume some SMART commands may be dangerous for the disks' >> data itself ? >> >> Thank you again, > On 23 Feb 2018, Scott Long wrote: > Sure, there are a finite number of SMART commands, even when you consider > variations for SAS and SATL. The commands aren’t explicitly flagged to > the kernel, but they can be parsed. You could even move the SMART logic > directly into the kernel. However, issuing the commands is often > disruptive to the system; for SATA, it’s a non-queueing command, so the > system has to drain and serialize I/O while it’s active. This can be > crudely used as a DOS attack. There are also SMART commands to do > long-running diagnostics, that while they’re not destructive, they can > still be disruptive. Also, SMART statistics can be used to gain insight > into the operation of the system, making it easier to predict I/O > patterns and employ other side-channel attacks. The point of > securelevel=2 is to prevent access to disk devices that can result in > system disruption, so I’m adverse to making an exception that’s directly > counter to that point. Thank you Scott. securelevel=2 really makes sense, as (IMO) SMART error reports / statistics and diagnostics. Hard to combine both actually. Perhaps a solution could be the SMART logic into the kernel, with the ability to disable it (compilation option ?). On 23 Feb 2018, Douglas Gilbert wrote: > A partial solution with big storage behind a storage switch (FC, PCIe or > SAS) is to run one machine *** (preferably not accessible directly from the > internet) at a lower privilege level that permits it to run smartmontools > and other similar utilities (such as a management utility for that > storage switch). Thank you Douglas, yes you're right, SAS shared JBODs would do the trick. Mine are SAS, but unfortunately local / not shared. Theses disks are parts of ZFS pools. Instead of running zpool scrubs each 2 weeks and SMART long self tests the other 2 weeks, I could run weekly zpool scrubs. But I think I will loose the opportunity to be notified by smartmontools about a pre-dying disk, in addition sectors not yet used by ZFS would not be tested. Thank you again, Ben
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