Date: Tue, 26 Jun 2018 15:45:57 +0200 From: Alexander Potapenko <glider@...gle.com> To: Vladis Dronov <vdronov@...hat.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 On Fri, Jun 22, 2018 at 3:32 PM Vladis Dronov <vdronov@...hat.com> wrote: > > Hello, Alexander, Hi Vladis, > 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; Yes, you're right. It appears unlikely that a user has both CAP_SYS_ADMIN and CAP_SYS_RAWIO. > 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. How do I proceed with this? > > Best regards, > Vladis Dronov | Red Hat, Inc. | Product Security Engineer Thank you, -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
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