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Date: Wed, 09 Oct 2013 15:00:14 -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 v3] vsprintf: Check real user/group id for %pK
On Thu, 2013-10-10 at 08:52 +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.
Please review the patch I sent you a little more.
> 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.
[]
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> @@ -1312,11 +1313,37 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> spec.field_width = default_width;
> return string(buf, end, "pK-error", spec);
> }
Move the interrupt tests and pK-error printk
into case 1:
It's the only case where CAP_SYSLOG needs to be
tested so it doesn't need to be above the switch.
> - if (!((kptr_restrict == 0) ||
> - (kptr_restrict == 1 &&
> - has_capability_noaudit(current, CAP_SYSLOG))))
> +
> + switch (kptr_restrict) {
> + case 0:
> + /* Always print %pK values */
> + break;
> + case 1: {
> + /*
> + * Only print the real pointer value if the current
> + * process has CAP_SYSLOG and is running with the
> + * same credentials it started with. This is because
> + * access to files is checked at open() time, but %pK
> + * checks permission at read() time. We don't want to
> + * leak pointer values if a binary opens a file using
> + * %pK and then elevates privileges before reading it.
> + */
> + const struct cred *cred = current_cred();
> +
> + if (!has_capability_noaudit(current, CAP_SYSLOG) ||
> + !uid_eq(cred->euid, cred->uid) ||
> + !gid_eq(cred->egid, cred->gid))
> + ptr = NULL;
> + break;
> + }
> + case 2:
> + default:
> + /* Always print 0's for %pK */
> ptr = NULL;
> + break;
> + }
> break;
> +
> case 'N':
> switch (fmt[1]) {
> case 'F':
>
>
> --
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