Date: Tue, 08 Oct 2013 19:00:56 -0700 From: Joe Perches <joe@...ches.com> To: Ryan Mallon <rmallon@...il.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, eldad@...refinery.com, Jiri Kosina <jkosina@...e.cz>, jgunthorpe@...idianresearch.com, Dan Rosenberg <dan.j.rosenberg@...il.com>, Kees Cook <keescook@...omium.org>, Alexander Viro <viro@...iv.linux.org.uk>, "Eric W. Biederman" <ebiederm@...ssion.com>, George Spelvin <linux@...izon.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2] vsprintf: Check real user/group id for %pK On Wed, 2013-10-09 at 12:55 +1100, Ryan Mallon wrote: > On 09/10/13 12:30, Joe Perches wrote: > > On Tue, 2013-10-08 at 17:49 -0700, Joe Perches wrote: > >> On Wed, 2013-10-09 at 11:15 +1100, Ryan Mallon wrote: > >>> Some setuid binaries will allow reading of files which have read > >>> permission by the real user id. This is problematic with files which > >>> use %pK because the file access permission is checked at open() time, > >>> but the kptr_restrict setting is checked at read() time. If a setuid > >>> binary opens a %pK file as an unprivileged user, and then elevates > >>> permissions before reading the file, then kernel pointer values may be > >>> leaked. > >> > >> I think it should explicitly test 0. > > > > Also, Documentation/sysctl/kernel.txt should be updated too. > > > > Here's a suggested patch: > > > > --- > > Documentation/sysctl/kernel.txt | 14 ++++++++------ > > lib/vsprintf.c | 38 ++++++++++++++++++++++++++------------ > > 2 files changed, 34 insertions(+), 18 deletions(-) > > > > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > > index 9d4c1d1..eac53d5 100644 > > --- a/Documentation/sysctl/kernel.txt > > +++ b/Documentation/sysctl/kernel.txt > > @@ -290,13 +290,15 @@ Default value is "/sbin/hotplug". > > kptr_restrict: > > > > This toggle indicates whether restrictions are placed on > > -exposing kernel addresses via /proc and other interfaces. When > > -kptr_restrict is set to (0), there are no restrictions. When > > -kptr_restrict is set to (1), the default, kernel pointers > > +exposing kernel addresses via /proc and other interfaces. > > + > > +When kptr_restrict is set to (0), there are no restrictions. > > +When kptr_restrict is set to (1), the default, kernel pointers > > printed using the %pK format specifier will be replaced with 0's > > -unless the user has CAP_SYSLOG. When kptr_restrict is set to > > -(2), kernel pointers printed using %pK will be replaced with 0's > > -regardless of privileges. > > +unless the user has CAP_SYSLOG and effective user and group ids > > +are equal to the real ids. > > +When kptr_restrict is set to (2), kernel pointers printed using > > +%pK will be replaced with 0's regardless of privileges. > > I'll add this, thanks. > > I'm less fussed about the suggestions for the logic. The current test is > small and concise. The logic ends up the same to the compiler, but it's human readers that want simple and clear. > The original also does the in_irq tests regardless of > the kptr_restrict setting since they are mostly intended to catch > internal kernel bugs. Not so. http://marc.info/?l=linux-security-module&m=129303800912245&w=4 https://lkml.org/lkml/2012/7/13/428
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