---

yaml
---
r: 221725
b: refs/heads/master
c: eaf06b2
h: refs/heads/master
i:
  221723: e6ec877
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 203f40a5a030ed4048cd40e3bd9ab5df6c5df589
+refs/heads/master: eaf06b241b091357e72b76863ba16e89610d31bd

trunk/Documentation/sysctl/kernel.txt

@@ -28,6 +28,7 @@ show up in /proc/sys/kernel:
 - core_uses_pid
 - ctrl-alt-del
 - dentry-state
+- dmesg_restrict
 - domainname
 - hostname
 - hotplug
@@ -213,6 +214,19 @@ to decide what to do with it.
 
 ==============================================================
 
+dmesg_restrict:
+
+This toggle indicates whether unprivileged users are prevented from using
+dmesg(8) to view messages from the kernel's log buffer.  When
+dmesg_restrict is set to (0) there are no restrictions.  When
+dmesg_restrict is set set to (1), users must have CAP_SYS_ADMIN to use
+dmesg(8).
+
+The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the default
+value of dmesg_restrict.
+
+==============================================================
+
 domainname & hostname:
 
 These files can be used to set the NIS/YP domainname and the

trunk/include/linux/kernel.h

@@ -293,6 +293,7 @@ extern bool printk_timed_ratelimit(unsigned long *caller_jiffies,
 				   unsigned int interval_msec);
 
 extern int printk_delay_msec;
+extern int dmesg_restrict;
 
 /*
  * Print a one-time message (analogous to WARN_ONCE() et al):

trunk/kernel/printk.c

@@ -261,6 +261,12 @@ static inline void boot_delay_msec(void)
 }
 #endif
 
+#ifdef CONFIG_SECURITY_DMESG_RESTRICT
+int dmesg_restrict = 1;
+#else
+int dmesg_restrict;
+#endif
+
 int do_syslog(int type, char __user *buf, int len, bool from_file)
 {
 	unsigned i, j, limit, count;

trunk/kernel/sysctl.c

@@ -703,6 +703,15 @@ static struct ctl_table kern_table[] = {
 		.extra2		= &ten_thousand,
 	},
 #endif
+	{
+		.procname	= "dmesg_restrict",
+		.data		= &dmesg_restrict,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
 	{
 		.procname	= "ngroups_max",
 		.data		= &ngroups_max,

trunk/security/Kconfig

@@ -39,6 +39,18 @@ config KEYS_DEBUG_PROC_KEYS
 
 	  If you are unsure as to whether this is required, answer N.
 
+config SECURITY_DMESG_RESTRICT
+	bool "Restrict unprivileged access to the kernel syslog"
+	default n
+	help
+	  This enforces restrictions on unprivileged users reading the kernel
+	  syslog via dmesg(8).
+
+	  If this option is not selected, no restrictions will be enforced
+	  unless the dmesg_restrict sysctl is explicitly set to (1).
+
+	  If you are unsure how to answer this question, answer N.
+
 config SECURITY
 	bool "Enable different security models"
 	depends on SYSFS

trunk/security/commoncap.c

@@ -895,6 +895,8 @@ int cap_syslog(int type, bool from_file)
 {
 	if (type != SYSLOG_ACTION_OPEN && from_file)
 		return 0;
+	if (dmesg_restrict && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
 	if ((type != SYSLOG_ACTION_READ_ALL &&
 	     type != SYSLOG_ACTION_SIZE_BUFFER) && !capable(CAP_SYS_ADMIN))
 		return -EPERM;