From: "Christian Göttsche" <cgzones@googlemail.com>
To: selinux@vger.kernel.org
Cc: Paul Moore <paul@paul-moore.com>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
Ondrej Mosnacek <omosnace@redhat.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/2] selinux: improve symtab string hashing
Date: Fri, 15 Mar 2024 19:14:04 +0100 [thread overview]
Message-ID: <20240315181414.649045-1-cgzones@googlemail.com> (raw)
The number of buckets is calculated by performing a binary AND against
the mask of the hash table, which is one less than its size (which is a
power of two). This leads to all top bits being discarded, requiring
for short or similar inputs a hash function with a good avalanche
effect.
Use djb2a:
# current
common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11
classes: 134 entries and 100/256 buckets used, longest chain length 5, sum of chain length^2 234
roles: 15 entries and 6/16 buckets used, longest chain length 5, sum of chain length^2 57
types: 4448 entries and 3016/8192 buckets used, longest chain length 41, sum of chain length^2 14922
users: 7 entries and 3/8 buckets used, longest chain length 3, sum of chain length^2 17
bools: 306 entries and 221/512 buckets used, longest chain length 4, sum of chain length^2 524
levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1
categories: 1024 entries and 400/1024 buckets used, longest chain length 4, sum of chain length^2 2740
# patch
common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11
classes: 134 entries and 101/256 buckets used, longest chain length 3, sum of chain length^2 210
roles: 15 entries and 9/16 buckets used, longest chain length 3, sum of chain length^2 31
types: 4448 entries and 3459/8192 buckets used, longest chain length 5, sum of chain length^2 6778
users: 7 entries and 5/8 buckets used, longest chain length 3, sum of chain length^2 13
bools: 306 entries and 236/512 buckets used, longest chain length 5, sum of chain length^2 470
levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1
categories: 1024 entries and 518/1024 buckets used, longest chain length 7, sum of chain length^2 2992
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
---
v2:
add licensing note
---
security/selinux/ss/symtab.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
diff --git a/security/selinux/ss/symtab.c b/security/selinux/ss/symtab.c
index c04f8d447873..832660fd84a9 100644
--- a/security/selinux/ss/symtab.c
+++ b/security/selinux/ss/symtab.c
@@ -12,17 +12,17 @@
static unsigned int symhash(const void *key)
{
- const char *p, *keyp;
- unsigned int size;
- unsigned int val;
-
- val = 0;
- keyp = key;
- size = strlen(keyp);
- for (p = keyp; (p - keyp) < size; p++)
- val = (val << 4 | (val >> (8 * sizeof(unsigned int) - 4))) ^
- (*p);
- return val;
+ /*
+ * djb2a
+ * Public domain from cdb v0.75
+ */
+ unsigned int hash = 5381;
+ unsigned char c;
+
+ while ((c = *(const unsigned char *)key++))
+ hash = ((hash << 5) + hash) ^ c;
+
+ return hash;
}
static int symcmp(const void *key1, const void *key2)
--
2.43.0
next reply other threads:[~2024-03-15 18:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-15 18:14 Christian Göttsche [this message]
2024-03-15 18:14 ` [PATCH v2 1/2] selinux: dump statistics for more hash tables Christian Göttsche
2024-03-27 23:26 ` Paul Moore
2024-03-27 23:26 ` [PATCH v2 2/2] selinux: improve symtab string hashing Paul Moore
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