[PATCH 1/1] Define CAP_SYSLOG

[PATCH 1/1] Define CAP_SYSLOG

[Serge E. Hallyn]

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 <serge.hallyn@ubuntu.com>
Acked-by: Andrew G. Morgan <morgan@kernel.org>
Acked-By: Kees Cook <kees.cook@canonical.com>
Cc: James Morris <jmorris@namei.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: "Christopher J. PeBenito" <cpebenito@tresys.com>
Cc: Eric Paris <eparis@parisplace.org>
---
 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

Re: [PATCH 1/1] Define CAP_SYSLOG

[Randy Dunlap]

On Thu, 25 Nov 2010 17:11:32 +0000 Serge E. Hallyn wrote:

> 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 <serge.hallyn@ubuntu.com>
> Acked-by: Andrew G. Morgan <morgan@kernel.org>
> Acked-By: Kees Cook <kees.cook@canonical.com>
> Cc: James Morris <jmorris@namei.org>
> Cc: Michael Kerrisk <mtk.manpages@gmail.com>
> Cc: Stephen Smalley <sds@tycho.nsa.gov>
> Cc: "Christopher J. PeBenito" <cpebenito@tresys.com>
> Cc: Eric Paris <eparis@parisplace.org>
> ---
>  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 */

	Is this supposed to say: after 2.6.38 ??

> +			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 } },
> -- 


---
~Randy
*** Remember to use Documentation/SubmitChecklist when testing your code ***

Re: [PATCH 1/1] Define CAP_SYSLOG

[Serge E. Hallyn]

Quoting Randy Dunlap (rdunlap@xenotime.net):
> On Thu, 25 Nov 2010 17:11:32 +0000 Serge E. Hallyn wrote:
> > +			/* remove after 2.6.28 */
> 
> 	Is this supposed to say: after 2.6.38 ??

:)  yup - i only noticed this after sending it, looking at
lkml.org, but didn't have a way of getting to my mail
server to reply to myself.

thanks,
-serge

Re: [PATCH 1/1] Define CAP_SYSLOG

[James Morris]

On Thu, 25 Nov 2010, Serge E. Hallyn wrote:

> 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

Applied with kernel version fix to:
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6#next

-- 
James Morris
<jmorris@namei.org>