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Gmane
From: Serge E. Hallyn <serge <at> hallyn.com>
Subject: [PATCH 1/1] Define CAP_SYSLOG
Newsgroups: gmane.linux.kernel
Date: Thursday 25th November 2010 17:11:32 UTC (over 6 years ago)
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).

Changelog: mar 12 2010: add selinux capability2:cap_syslog perm
Changelog: nov 22 2010:
	. port to new kernel
	. add a WARN_ONCE if userspace isn't using CAP_SYSLOG

Signed-off-by: Serge Hallyn 
Acked-by: Andrew G. Morgan 
Acked-By: Kees Cook 
Cc: James Morris <[email protected]>
Cc: Michael Kerrisk 
Cc: Stephen Smalley 
Cc: "Christopher J. PeBenito" 
Cc: Eric Paris 
---
 include/linux/capability.h          |    7 +++++--
 kernel/printk.c                     |    8 +++++++-
 security/selinux/include/classmap.h |    2 +-
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 90012b9..fb16a36 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -246,7 +246,6 @@ 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() */
@@ -352,7 +351,11 @@ 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/kernel/printk.c b/kernel/printk.c
index 9a2264f..111cdc2 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -283,8 +283,14 @@ int do_syslog(int type, char __user *buf, int len,
bool from_file)
 			return -EPERM;
 		if ((type != SYSLOG_ACTION_READ_ALL &&
 		     type != SYSLOG_ACTION_SIZE_BUFFER) &&
-		    !capable(CAP_SYS_ADMIN))
+		    !capable(CAP_SYSLOG)) {
+			/* remove after 2.6.28 */
+			if (capable(CAP_SYS_ADMIN))
+				WARN_ONCE(1, "Attempt to access syslog with "
+				  "CAP_SYS_ADMIN but no CAP_SYSLOG "
+				  "(deprecated and denied).\n");
 			return -EPERM;
+		}
 	}
 
 	error = security_syslog(type);
diff --git a/security/selinux/include/classmap.h
b/security/selinux/include/classmap.h
index 8858d2b..7ed3663 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 } },
-- 
1.7.0.4

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