Date: Wed, 4 Oct 2017 21:13:39 +0200 From: Jann Horn <jannh@...gle.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Kees Cook <keescook@...omium.org>, "Tobin C. Harding" <me@...in.cc>, Greg KH <gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>, William Roberts <william.c.roberts@...el.com>, Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com> Subject: Re: [RFC V2 4/6] lib: vsprintf: default kptr_restrict to the maximum value On Wed, Oct 4, 2017 at 7:28 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Wed, Oct 4, 2017 at 10:08 AM, Linus Torvalds > <torvalds@...ux-foundation.org> wrote: >> >> So I honestly doubt the value of kptr_restrict. Any *sane* policy >> pretty much has to be in the caller, and by thinking about what you >> print out. IOW, things like proc_pid_wchan(). > > Looking at /proc/kallsyms is actually a prime example of this. > > IOW, the old "open /proc/kallsyms as a normal user, then make it stdin > for some suid-root program that can be fooled to output it probably > works on it. Actually, /proc/kallsyms uses %pK, which hacks around this issue by checking for `euid != uid` in addition to the capability check - so this isn't exploitable through a typical setuid program.
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