Date: Tue, 20 Mar 2012 10:11:02 -0700 From: Kees Cook <keescook@...omium.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: Serge Hallyn <serge.hallyn@...onical.com>, linux-kernel@...r.kernel.org, Darren Hart <dvhart@...ux.intel.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Andrew Morton <akpm@...ux-foundation.org>, Jiri Kosina <jkosina@...e.cz>, "Eric W. Biederman" <ebiederm@...ssion.com>, David Howells <dhowells@...hat.com>, kernel-hardening@...ts.openwall.com, spender@...ecurity.net, mingo@...nel.org Subject: Re: [PATCH] futex: do not leak robust list to unprivileged process On Tue, Mar 20, 2012 at 10:02 AM, Thomas Gleixner <tglx@...utronix.de> wrote: > On Tue, 20 Mar 2012, Serge Hallyn wrote: > >> Quoting Kees Cook (keescook@...omium.org): >> > It was possible to extract the robust list head address from a setuid >> > process if it had used set_robust_list(), allowing an ASLR info leak. This >> > changes the permission checks to be the same as those used for similar >> > info that comes out of /proc. >> > >> > Running a setuid program that uses robust futexes would have had: >> > cred->euid != pcred->euid >> > cred->euid == pcred->uid >> > so the old permissions check would allow it. I'm not aware of any setuid >> > programs that use robust futexes, so this is just a preventative measure. >> > >> > (This patch is based on changes from grsecurity.) >> > >> > Signed-off-by: Kees Cook <keescook@...omium.org> >> >> I like the change. Much cleaner. I'm not 100% sure though that >> there are no legitimate cases of robust futexes use which would now >> be forbidden. (Explicitly cc:ing Ingo) > > get_robust_list is not necessary for robust futexes. There is no > reference to get_robust_list in glibc. > > I really wonder why we have this syscall at all. The documentation I found yesterday while looking at this was: http://linux.die.net/man/2/get_robust_list Which says "The system call is only available for debugging purposes and is not needed for normal operations. Both system calls are not available to application programs as functions; they can be called using the syscall(3) function." Dropping the syscall entirely would certainly make it secure. ;) -Kees -- Kees Cook ChromeOS Security
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