Date: Tue, 5 Nov 2019 08:07:30 +0100 From: Salvatore Bonaccorso <carnil@...ian.org> To: oss-security@...ts.openwall.com Subject: Re: [ Linux kernel ] Exploitable bugs in drivers/media/platform/vivid Hi, On Sat, Nov 02, 2019 at 10:27:27PM +0300, Alexander Popov wrote: > Hello! > > I used the syzkaller fuzzer with custom modifications and found a bunch of > 5-year old bugs in the Linux kernel. I managed to exploit one of them for a > local privilege escalation. > > These vulnerabilities are caused by wrong mutex locking in the vivid driver of > the V4L2 subsystem. Please see the fixing patch that I've just sent to LKML: > https://firstname.lastname@example.org/ > > The vivid driver doesn't require any special hardware. It is shipped in Ubuntu, > Debian, Arch Linux, SUSE Linux Enterprise and openSUSE. > > On Ubuntu the devices created by this driver are available to the normal user, > since Ubuntu applies RW ACL when the user is logged in: > a13x@...ntu_server_1804:~$ getfacl /dev/video0 > getfacl: Removing leading '/' from absolute path names > # file: dev/video0 > # owner: root > # group: video > user::rw- > user:a13x:rw- > group::rw- > mask::rw- > other::--- > > (Un)fortunately, I don't know how to autoload the vulnerable driver, which > limits the severity of these vulnerabilities. That's why the Linux kernel > security team allows me to do the full disclosure. > > But there is an interesting aspect -- my PoC exploit bypasses SMEP and SMAP on > the fresh Ubuntu Server 18.04. Moreover, it gains the local privilege escalation > from the kthread context (where the userspace is not mapped). I'm going to share > the details about the exploit techniques later. > > For now I would recommend to blacklist the vivid kernel module on your machines. CVE-2019-18683 was assigned for this issue. Regards, Salvatore
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