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authorDan Rosenberg <drosenberg@vsecurity.com>2011-01-12 16:59:41 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 08:03:08 -0800
commit455cd5ab305c90ffc422dd2e0fb634730942b257 (patch)
treec20e6c3f8e58967991ce9002abe03d31897b171c /Documentation/sysctl
parent351f8f8e6499ae4fff40f5e3a8fe16d9e1903646 (diff)
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 <drosenberg@vsecurity.com> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: James Morris <jmorris@namei.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Thomas Graf <tgraf@infradead.org> Cc: Eugene Teo <eugeneteo@kernel.org> Cc: Kees Cook <kees.cook@canonical.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David S. Miller <davem@davemloft.net> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Eric Paris <eparis@parisplace.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/sysctl')
-rw-r--r--Documentation/sysctl/kernel.txt14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 574067194f3..11d5ceda5bb 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -34,6 +34,7 @@ show up in /proc/sys/kernel:
- hotplug
- java-appletviewer [ binfmt_java, obsolete ]
- java-interpreter [ binfmt_java, obsolete ]
+- kptr_restrict
- kstack_depth_to_print [ X86 only ]
- l2cr [ PPC only ]
- modprobe ==> Documentation/debugging-modules.txt
@@ -261,6 +262,19 @@ This flag controls the L2 cache of G3 processor boards. If
==============================================================
+kptr_restrict:
+
+This toggle indicates whether restrictions are placed on
+exposing kernel addresses via /proc and other interfaces. When
+kptr_restrict is set to (0), there are no restrictions. When
+kptr_restrict is set to (1), the default, kernel pointers
+printed using the %pK format specifier will be replaced with 0's
+unless the user has CAP_SYSLOG. When kptr_restrict is set to
+(2), kernel pointers printed using %pK will be replaced with 0's
+regardless of privileges.
+
+==============================================================
+
kstack_depth_to_print: (X86 only)
Controls the number of words to print when dumping the raw