Date: Fri, 29 Jan 2021 18:01:11 +0100 From: Marcus Meissner <meissner@...e.de> To: oss-security@...ts.openwall.com Subject: Re: Linux Kernel: local priv escalation via futexes Hi, Mitre has now assigned CVE-2021-3347. On Fri, Jan 29, 2021 at 05:42:08PM +0100, Solar Designer wrote: > Hi, > > I'm not familiar with futexes, but just to save others a few minutes on > looking this up: (Is anyone? Futex are too complex for me at least, I would guess also using them is error prone.) > On Fri, Jan 29, 2021 at 11:09:28AM +0100, Marcus Meissner wrote: > > - Address a longstanding issue where the user space part of the PI > > futex is not writeable. The kernel returns with inconsistent state > > which can in the worst case result in a UAF of a tasks kernel > > stack. > > > > The solution is to establish consistent kernel state which makes > > future operations on the futex fail because user space and kernel > > space state are inconsistent. Not a problem as PI futexes > > fundamentaly require a functional RW mapping and if user space > > pulls the rug under it, then it can keep the pieces it asked for. > > > * tag 'locking-urgent-2021-01-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: > > futex: Handle faults correctly for PI futexes > > FWIW, this commit has: > > Fixes: 1b7558e457ed ("futexes: fix fault handling in futex_lock_pi") > > and that other commit is from 2008. So probably all currently > maintained Linux distros and deployments are affected, unless something > else mitigated the issue in some kernel versions. Yes, goes back to a long history, sorry for leaving this out. Ciao, Marcus
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