linux-kernel - Re: [PATCH 5.10 083/102] scsi: iscsi: Restrict sessions and handles to admin capabilities

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Date:   Fri, 5 Mar 2021 16:05:26 -0800
From:   Lee Duncan <lduncan@...e.com>
To:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Adam Nichols <adam@...mm-co.com>,
        Chris Leech <cleech@...hat.com>,
        Mike Christie <michael.christie@...cle.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH 5.10 083/102] scsi: iscsi: Restrict sessions and handles
 to admin capabilities

On 3/5/21 2:42 PM, Pavel Machek wrote:
> Hi!
> 
>> From: Lee Duncan <lduncan@...e.com>
>>
>> commit 688e8128b7a92df982709a4137ea4588d16f24aa upstream.
>>
>> Protect the iSCSI transport handle, available in sysfs, by requiring
>> CAP_SYS_ADMIN to read it. Also protect the netlink socket by restricting
>> reception of messages to ones sent with CAP_SYS_ADMIN. This disables
>> normal users from being able to end arbitrary iSCSI sessions.
> 
> Should not normal filesystem permissions be used?
> 
>> +++ b/drivers/scsi/scsi_transport_iscsi.c
>> @@ -132,6 +132,9 @@ show_transport_handle(struct device *dev
>>  		      char *buf)
>>  {
>>  	struct iscsi_internal *priv = dev_to_iscsi_internal(dev);
>> +
>> +	if (!capable(CAP_SYS_ADMIN))
>> +		return -EACCES;
>>  	return sprintf(buf, "%llu\n", (unsigned long long)iscsi_handle(priv->iscsi_transport));
>>  }
>>  static DEVICE_ATTR(handle, S_IRUGO, show_transport_handle, NULL);
> 
> AFAICT we make the file 0444 (world readable) and then fail the read
> with capability check. If the file is not supposed to be
> world-readable, it should have 0400 permissions, right?
> 
> Best regards,
> 								Pavel
> 

I am ok with changing file permissions, but there's nothing wrong with
checking capabilities upon entry, as well, since capability checks are a
higher degree of security than ACLs.
-- 
Lee Duncan