Date: Fri, 22 Jun 2018 09:32:43 -0400 (EDT) From: Vladis Dronov <vdronov@...hat.com> To: Alexander Potapenko <glider@...gle.com> Cc: oss-security@...ts.openwall.com Subject: Re: CVE-2018-1000204: Linux kernel 3.18 to 4.16 infoleak due to incorrect handling of SG_IO ioctl Hello, Alexander, Could you please, explain, why do you think CVE-2018-1000204 is a security flaw? > The problem has limited scope, as users don't usually have permissions > to access SCSI devices. On the other hand, e.g. the Nero user manual > suggests doing `chmod o+r+w /dev/sg*` to make the devices accessible. There is a check in the kernel in sg_build_indirect() exactly for this situation: [drivers/scsi/sg.c] if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO)) gfp_mask |= __GFP_ZERO; This means non-root user will get zero-ed pages even if it has o+rw access to /dev/sg*. Tests of your reproducer on systems available to me confirm this, i.e. non-root user gets a zero-ed out buffer even if it is able to access /dev/sg*. I may not got smth correctly, but for now I do not see CVE-2018-1000204 as a security flaw and I believe a reject request to MITRE should be issued. Best regards, Vladis Dronov | Red Hat, Inc. | Product Security Engineer
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