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authorDan Rosenberg <drosenberg@vsecurity.com>2010-11-11 17:05:18 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2010-11-12 10:55:32 -0500
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')
-rw-r--r--kernel/printk.c6
-rw-r--r--kernel/sysctl.c9
2 files changed, 15 insertions, 0 deletions
diff --git a/kernel/printk.c b/kernel/printk.c
index b2ebaee8c377..38e7d5868d60 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -261,6 +261,12 @@ static inline void boot_delay_msec(void)
261} 261}
262#endif 262#endif
263 263
264#ifdef CONFIG_SECURITY_DMESG_RESTRICT
265int dmesg_restrict = 1;
266#else
267int dmesg_restrict;
268#endif
269
264int do_syslog(int type, char __user *buf, int len, bool from_file) 270int do_syslog(int type, char __user *buf, int len, bool from_file)
265{ 271{
266 unsigned i, j, limit, count; 272 unsigned i, j, limit, count;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c33a1edb799f..b65bf634035e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -704,6 +704,15 @@ static struct ctl_table kern_table[] = {
704 }, 704 },
705#endif 705#endif
706 { 706 {
707 .procname = "dmesg_restrict",
708 .data = &dmesg_restrict,
709 .maxlen = sizeof(int),
710 .mode = 0644,
711 .proc_handler = proc_dointvec_minmax,
712 .extra1 = &zero,
713 .extra2 = &one,
714 },
715 {
707 .procname = "ngroups_max", 716 .procname = "ngroups_max",
708 .data = &ngroups_max, 717 .data = &ngroups_max,
709 .maxlen = sizeof (int), 718 .maxlen = sizeof (int),