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Message-Id: <20131015135113.ffdbeb97b73db061040904c9@linux-foundation.org>
Date: Tue, 15 Oct 2013 13:51:13 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Ryan Mallon <rmallon@...il.com>
Cc: Linus Torvalds <torvalds@...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>, Joe Perches
<joe@...ches.com>, "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, Rob Landley <rob@...dley.net>, Ingo Molnar
<mingo@...e.hu>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v4] vsprintf: Check real user/group id for %pK
On Tue, 15 Oct 2013 09:38:48 +1100 Ryan Mallon <rmallon@...il.com> 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.
>
> This happens for example with the setuid pppd application on Ubuntu 12.04:
>
> $ head -1 /proc/kallsyms
> 00000000 T startup_32
>
> $ pppd file /proc/kallsyms
> pppd: In file /proc/kallsyms: unrecognized option 'c1000000'
>
> This will only leak the pointer value from the first line, but other
> setuid binaries may leak more information.
>
> Fix this by adding a check that in addition to the current process
> having CAP_SYSLOG, that effective user and group ids are equal to the
> real ids. If a setuid binary reads the contents of a file which uses
> %pK then the pointer values will be printed as NULL if the real user
> is unprivileged.
>
> Update the sysctl documentation to reflect the changes, and also
> correct the documentation to state the kptr_restrict=0 is the default.
>
> This is a only temporary solution to the issue. The correct solution
> is to do the permission check at open() time on files, and to replace
> %pK with a function which checks the open() time permission. %pK uses
> in printk should be removed since no sane permission check can be
> done, and instead protected by using dmesg_restrict.
I grabbed this and queued it for 3.13-rc1, marked for backporting into
-stable. Given the amount of churn on this one I think it would be
imprudent to put it into mainline immediately.
I haven't been following the discussion very closely, so if anyone
thinks it should be ungrabbed, please speak up.
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