From 455cd5ab305c90ffc422dd2e0fb634730942b257 Mon Sep 17 00:00:00 2001 From: Dan Rosenberg Date: Wed, 12 Jan 2011 16:59:41 -0800 Subject: kptr_restrict for hiding kernel pointers from unprivileged users Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict sysctl. The %pK format specifier is designed to hide exposed kernel pointers, specifically via /proc interfaces. Exposing these pointers provides an easy target for kernel write vulnerabilities, since they reveal the locations of writable structures containing easily triggerable function pointers. The behavior of %pK depends on the kptr_restrict sysctl. If kptr_restrict is set to 0, no deviation from the standard %p behavior occurs. If kptr_restrict is set to 1, the default, if the current user (intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG (currently in the LSM tree), kernel pointers using %pK are printed as 0's. If kptr_restrict is set to 2, kernel pointers using %pK are printed as 0's regardless of privileges. Replacing with 0's was chosen over the default "(null)", which cannot be parsed by userland %p, which expects "(nil)". [akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/] [akpm@linux-foundation.org: coding-style fixup] [randy.dunlap@oracle.com: fix kernel/sysctl.c warning] Signed-off-by: Dan Rosenberg Signed-off-by: Randy Dunlap Cc: James Morris Cc: Eric Dumazet Cc: Thomas Graf Cc: Eugene Teo Cc: Kees Cook Cc: Ingo Molnar Cc: David S. Miller Cc: Peter Zijlstra Cc: Eric Paris Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/printk.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/printk.h') diff --git a/include/linux/printk.h b/include/linux/printk.h index b772ca5fbdf0..9adfba6ec28a 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -83,6 +83,7 @@ extern bool printk_timed_ratelimit(unsigned long *caller_jiffies, extern int printk_delay_msec; extern int dmesg_restrict; +extern int kptr_restrict; /* * Print a one-time message (analogous to WARN_ONCE() et al): -- cgit v1.2.1