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-rw-r--r--Documentation/sysctl/kernel.txt14
-rw-r--r--include/linux/kernel.h1
-rw-r--r--kernel/printk.c6
-rw-r--r--kernel/sysctl.c9
-rw-r--r--security/Kconfig12
-rw-r--r--security/commoncap.c2
6 files changed, 44 insertions, 0 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 3894eaa2348..209e1584c3d 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/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
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index b526947bdf4..fc3da9e4da1 100644
--- a/include/linux/kernel.h
+++ b/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):
diff --git a/kernel/printk.c b/kernel/printk.c
index b2ebaee8c37..38e7d5868d6 100644
--- a/kernel/printk.c
+++ b/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;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c33a1edb799..b65bf634035 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -704,6 +704,15 @@ static struct ctl_table kern_table[] = {
},
#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,
.maxlen = sizeof (int),
diff --git a/security/Kconfig b/security/Kconfig
index bd72ae62349..e80da955e68 100644
--- a/security/Kconfig
+++ b/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
diff --git a/security/commoncap.c b/security/commoncap.c
index 5e632b4857e..04b80f9912b 100644
--- a/security/commoncap.c
+++ b/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;