linux-kernel - [PATCH] Define CAP

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Date:	Fri, 12 Mar 2010 14:55:37 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	James Morris <jmorris@...ei.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	SELinux <selinux@...ho.nsa.gov>,
	linux-security-module@...r.kernel.org,
	Stephen Smalley <sds@...ch.ncsc.mil>,
	Kees Cook <kees.cook@...onical.com>,
	Andrew Morgan <morgan@...nel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"Christopher J. PeBenito" <cpebenito@...sys.com>,
	Eric Paris <eparis@...isplace.org>
Subject: [PATCH] Define CAP_SYSLOG

Privileged syslog operations currently require CAP_SYS_ADMIN.  Split
this off into a new CAP_SYSLOG privilege which we can sanely take away
from a container through the capability bounding set.

With this patch, an lxc container can be prevented from messing with
the host's syslog (i.e. dmesg -c).

There is one downside to this patch:  If some site or distro currently
has syslogd/whatever running as a non-root user with cap_sys_admin+pe,
then it will need to be changed to run with cap_syslog+pe.  I don't
know if there are such sites, or if that concern means we should take
a different approach to introducing this change, or simply refuse this
change.

I'm also sending out corresponding patches for libcap and refpolicy, and
will whip up a man-pages patch next week.

Changelog: mar 12 2010: add selinux capability2:cap_syslog perm

Signed-off-by: Serge E. Hallyn <serue@...ibm.com>
Acked-by: Andrew G. Morgan <morgan@...nel.org>
Acked-By: Kees Cook <kees.cook@...onical.com>
Cc: James Morris <jmorris@...ei.org>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Cc: Stephen Smalley <sds@...ho.nsa.gov>
Cc: "Christopher J. PeBenito" <cpebenito@...sys.com>
Cc: Eric Paris <eparis@...isplace.org>
---
 include/linux/capability.h          |    7 +++++--
 security/commoncap.c                |    2 +-
 security/selinux/include/classmap.h |    2 +-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 39e5ff5..837a55c 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -249,7 +249,6 @@ struct cpu_vfs_cap_data {
 /* Allow configuration of the secure attention key */
 /* Allow administration of the random device */
 /* Allow examination and configuration of disk quotas */
-/* Allow configuring the kernel's syslog (printk behaviour) */
 /* Allow setting the domainname */
 /* Allow setting the hostname */
 /* Allow calling bdflush() */
@@ -355,7 +354,11 @@ struct cpu_vfs_cap_data {
 
 #define CAP_MAC_ADMIN        33
 
-#define CAP_LAST_CAP         CAP_MAC_ADMIN
+/* Allow configuring the kernel's syslog (printk behaviour) */
+
+#define CAP_SYSLOG           34
+
+#define CAP_LAST_CAP         CAP_SYSLOG
 
 #define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
 
diff --git a/security/commoncap.c b/security/commoncap.c
index 6166973..018985e 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -899,7 +899,7 @@ int cap_syslog(int type, bool from_file)
 	if (type != SYSLOG_ACTION_OPEN && from_file)
 		return 0;
 	if ((type != SYSLOG_ACTION_READ_ALL &&
-	     type != SYSLOG_ACTION_SIZE_BUFFER) && !capable(CAP_SYS_ADMIN))
+	     type != SYSLOG_ACTION_SIZE_BUFFER) && !capable(CAP_SYSLOG))
 		return -EPERM;
 	return 0;
 }
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 8b32e95..f03cf56 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -142,7 +142,7 @@ struct security_class_mapping secclass_map[] = {
 	    "node_bind", "name_connect", NULL } },
 	{ "memprotect", { "mmap_zero", NULL } },
 	{ "peer", { "recv", NULL } },
-	{ "capability2", { "mac_override", "mac_admin", NULL } },
+	{ "capability2", { "mac_override", "mac_admin", "syslog", NULL } },
 	{ "kernel_service", { "use_as_override", "create_files_as", NULL } },
 	{ "tun_socket",
 	  { COMMON_SOCK_PERMS, NULL } },
-- 
1.6.1

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