selinux: Use a better hash function for avtab

This function, based on murmurhash3, has much better distribution than
the original. Using the current default of 2048 buckets, there are many
fewer collisions:

Before:
101421 entries and 2048/2048 buckets used, longest chain length 374
After:
101421 entries and 2048/2048 buckets used, longest chain length 81

The difference becomes much more significant when buckets are increased.
A naive attempt to expand the current function to larger outputs doesn't
yield any significant improvement; so this function is a prerequisite
for increasing the bucket size.

sds:  Adapted from the original patches for libsepol to the kernel.

Signed-off-by: John Brooks <john.brooks@jolla.com>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <pmoore@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/security/selinux/ss/avtab.h b/security/selinux/ss/avtab.h
index 9318b2b8f6c9..6d794a2eee57 100644
--- a/security/selinux/ss/avtab.h
+++ b/security/selinux/ss/avtab.h
@@ -56,7 +56,7 @@ struct avtab {
 	struct flex_array *htable;
 	u32 nel;	/* number of elements */
 	u32 nslot;      /* number of hash slots */
-	u16 mask;       /* mask to compute hash func */
+	u32 mask;       /* mask to compute hash func */
 
 };