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Message-ID: <5255E446.2000400@gmail.com>
Date: Thu, 10 Oct 2013 10:18:30 +1100
From: Ryan Mallon <rmallon@...il.com>
To: Joe Perches <joe@...ches.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 v3a] vsprintf: Check real user/group id for %pK
On 10/10/13 10:09, Joe Perches wrote:
> Changes in V3a:
>
> Do the in_irq tests only when kptr_restrict is 1.
> Document the %pK mechanism in vsnprintf
> Add missing documentation for %pV and %pNF too
I really did mean post a follow-up/separate patch, not a different
version of mine. The missing documentation for %pV and %pNF fix is fine,
but does not belong in this patch. The kptr_restrict pK-error is a
separate issue, my patch deliberately did not touch it because it is
unrelated. If you want to change it, please do so in a seperate patch.
You also removed my comment explaining why the uid/gid check is
necessary :-/.
~Ryan
> Documentation/sysctl/kernel.txt | 17 ++++++++--------
> lib/vsprintf.c | 43 ++++++++++++++++++++++++++++-------------
> 2 files changed, 39 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index 9d4c1d1..c17d5ca 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -289,14 +289,15 @@ 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
> -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.
> +This toggle indicates whether restrictions are placed on exposing kernel
> +addresses via /proc and other interfaces.
> +
> +When kptr_restrict is set to (0), the default, there are no restrictions.
> +When kptr_restrict is set to (1), kernel pointers printed using the %pK
> +format specifier will be replaced with 0's 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.
>
> ==============================================================
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 26559bd..3efcf29 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -27,6 +27,7 @@
> #include <linux/uaccess.h>
> #include <linux/ioport.h>
> #include <linux/dcache.h>
> +#include <linux/cred.h>
> #include <net/addrconf.h>
>
> #include <asm/page.h> /* for PAGE_SIZE */
> @@ -1301,21 +1302,34 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> va_end(va);
> return buf;
> }
> - case 'K':
> - /*
> - * %pK cannot be used in IRQ context because its test
> - * for CAP_SYSLOG would be meaningless.
> - */
> - if (kptr_restrict && (in_irq() || in_serving_softirq() ||
> - in_nmi())) {
> - if (spec.field_width == -1)
> - spec.field_width = default_width;
> - return string(buf, end, "pK-error", spec);
> + case 'K': /* see: Documentation/sysctl/kernel.txt */
> + switch (kptr_restrict) {
> + case 0: /* None (default) */
> + break;
> + case 1: { /* Restricted */
> + const struct cred *cred;
> +
> + if (in_irq() || in_serving_softirq() || in_nmi()) {
> + /*
> + * This cannot be used in IRQ context because
> + * the test for CAP_SYSLOG would be meaningless
> + */
> + if (spec.field_width == -1)
> + spec.field_width = default_width;
> + return string(buf, end, "pK-error", spec);
> + }
> + 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;
> }
> - if (!((kptr_restrict == 0) ||
> - (kptr_restrict == 1 &&
> - has_capability_noaudit(current, CAP_SYSLOG))))
> + case 2: /* Never - Always emit 0 */
> + default:
> ptr = NULL;
> + break;
> + }
> break;
> case 'N':
> switch (fmt[1]) {
> @@ -1574,6 +1588,9 @@ qualifier:
> * %piS depending on sa_family of 'struct sockaddr *' print IPv4/IPv6 address
> * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper
> * case.
> + * %pV recurse and output a struct va_format (const char *fmt, va_list *)
> + * %pK output a kernel address or 0 depending on sysctl kptr_restrict
> + * %pNF output a netdev_features_t
> * %*ph[CDN] a variable-length hex string with a separator (supports up to 64
> * bytes of the input)
> * %n is ignored
>
>
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