linux-kernel - Re: [PATCH v2] block: avoid false positive warnings on ioctl to partition

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Message-ID: <4F4B78CE.4010405@redhat.com>
Date:	Mon, 27 Feb 2012 13:36:30 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	stable@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v2] block: avoid false positive warnings on ioctl to partition

Ping.

On 02/17/2012 08:38 AM, Paolo Bonzini wrote:
> After a month of reports, the warnings from non-whitelisted ioctls to
> a partitions can be classified in three groups.
> 
> BLKFLSBUF and BLKROSET are always sent to devices.  Not having them in
> the whitelist did not cause any visible harm, but anyway they can and
> should be added to the whitelist.
> 
> Many unrecognized ioctls are sent to partitions as an attempt to probe for
> CD-ROMs, floppies and other kinds of devices.  Like CDROM_GET_CAPABILITY,
> they can be blocked safely.
> 
> Of the actual SCSI ioctls, only SG_IO was reported in the wild (twice).
> udev's scsi_id can issue INQUIRY commands if passed a partition; this
> only occurs with custom rules and is strictly speaking invalid, but we
> need a transition period so that people can fix their configuration.
> zfs-fuse also can issue SYNCHRONIZE CACHE commands, where it should
> simply use fdatasync.
> 
> Therefore, this patch silently blocks all ioctls except SG_IO, since
> all of them turned out to be false positives; in case some escaped, it
> should be easily diagnosable or at least bisectable.  The warning text
> is separated for root and non-root.  The warning for SG_IO is left in
> because a) it will alert users to possible bugs, and b) we do want to
> hear about more uses in the wild.  However, no deprecation period is
> set for now.
> 
> Cc: stable@...r.kernel.org
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
> 	Note: I will take care of the stable backport as soon as this
> 	patch or something similar hits Linus's tree.
> 
>  block/scsi_ioctl.c |   40 ++++++++++++++++++++++++++++++-------------
>  1 files changed, 27 insertions(+), 13 deletions(-)
> 
> diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
> index 260fa80..fe86923 100644
> --- a/block/scsi_ioctl.c
> +++ b/block/scsi_ioctl.c
> @@ -696,9 +696,6 @@ int scsi_verify_blk_ioctl(struct block_device *bd, unsigned int cmd)
>  	if (bd && bd == bd->bd_contains)
>  		return 0;
>  
> -	/* Actually none of these is particularly useful on a partition,
> -	 * but they are safe.
> -	 */
>  	switch (cmd) {
>  	case SCSI_IOCTL_GET_IDLUN:
>  	case SCSI_IOCTL_GET_BUS_NUMBER:
> @@ -710,22 +707,39 @@ int scsi_verify_blk_ioctl(struct block_device *bd, unsigned int cmd)
>  	case SG_GET_RESERVED_SIZE:
>  	case SG_SET_RESERVED_SIZE:
>  	case SG_EMULATED_HOST:
> +		/* Actually none of these is particularly useful on a partition,
> +		 * but they are safe.
> +		 */
>  		return 0;
> -	case CDROM_GET_CAPABILITY:
> -		/* Keep this until we remove the printk below.  udev sends it
> -		 * and we do not want to spam dmesg about it.   CD-ROMs do
> -		 * not have partitions, so we get here only for disks.
> -		 */
> -		return -ENOIOCTLCMD;
> +
> +	case BLKROSET:
> +	case BLKFLSBUF:
> +		/* These are generic block layer ioctls that are nevertheless
> +		 * passed down to devices.  They are certainly valid for
> +		 * partitions!
> +		 */
> +		return 0;
> +
> +	case SG_IO:
> +		/* Accept this for root users, at least for now.  */
> +		break;
> +
>  	default:
> -		break;
> +		/* In particular, rule out resets and host-specific ioctls.  */
> +		return -ENOIOCTLCMD;
>  	}
>  
> -	/* In particular, rule out all resets and host-specific ioctls.  */
> -	printk_ratelimited(KERN_WARNING
> -			   "%s: sending ioctl %x to a partition!\n", current->comm, cmd);
> +	if (capable(CAP_SYS_RAWIO)) {
> +		printk_ratelimited(KERN_WARNING
> +				   "%s: SG_IO to a partition is likely a bug\n",
> +				   current->comm);
> +		return 0;
> +	}
>  
> -	return capable(CAP_SYS_RAWIO) ? 0 : -ENOIOCTLCMD;
> +	printk_ratelimited(KERN_WARNING
> +			   "%s: rejecting SG_IO to a partition for non-root user\n",
> +			   current->comm);
> +	return -ENOIOCTLCMD;
>  }
>  EXPORT_SYMBOL(scsi_verify_blk_ioctl);
>  

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