diff options
| author | Christian Göttsche <cgzones@googlemail.com> | 2024-03-15 19:14:04 +0100 |
|---|---|---|
| committer | Paul Moore <paul@paul-moore.com> | 2024-03-27 19:26:25 -0400 |
| commit | 32db469edfcca8f12b85299bb9311b9004c4e1ac (patch) | |
| tree | 2e8aaf3c7287fa603dceb024fe51103d518a68d3 /security/selinux | |
| parent | 0fd0b4fefaf04d62fca874413918cdee78bbe905 (diff) | |
selinux: improve symtab string hashing
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>
[PM: line length fixes in the commit message]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Diffstat (limited to 'security/selinux')
| -rw-r--r-- | security/selinux/ss/symtab.c | 22 |
1 files 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) |