path: root/kernel
diff options
authorDan Rosenberg <drosenberg@vsecurity.com>2010-11-11 14:05:18 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2010-11-12 07:55:32 -0800
commiteaf06b241b091357e72b76863ba16e89610d31bd (patch)
tree83bc8667309050b3538630707513574c14c51f37 /kernel
parent203f40a5a030ed4048cd40e3bd9ab5df6c5df589 (diff)
Restrict unprivileged access to kernel syslog
The kernel syslog contains debugging information that is often useful during exploitation of other vulnerabilities, such as kernel heap addresses. Rather than futilely attempt to sanitize hundreds (or thousands) of printk statements and simultaneously cripple useful debugging functionality, it is far simpler to create an option that prevents unprivileged users from reading the syslog. This patch, loosely based on grsecurity's GRKERNSEC_DMESG, creates the dmesg_restrict sysctl. When set to "0", the default, no restrictions are enforced. When set to "1", only users with CAP_SYS_ADMIN can read the kernel syslog via dmesg(8) or other mechanisms. [akpm@linux-foundation.org: explain the config option in kernel.txt] Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Acked-by: Ingo Molnar <mingo@elte.hu> Acked-by: Eugene Teo <eugeneteo@kernel.org> Acked-by: Kees Cook <kees.cook@canonical.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
2 files changed, 15 insertions, 0 deletions
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)
+int dmesg_restrict = 1;
+int dmesg_restrict;
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[] = {
+ .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),