54 lines
1.6 KiB
Diff
54 lines
1.6 KiB
Diff
From f1178a13dc8bc9e750cf59de1db8fc48867f9293 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Christian=20G=C3=B6ttsche?= <cgzones@googlemail.com>
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Date: Wed, 16 Aug 2023 14:38:44 +0200
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Subject: [PATCH] libselinux: use DJB2a string hash function
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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The hash table implementation uses `& (SIDTAB_SIZE - 1)` to truncate
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generated hashes to the number of buckets. This operation is equal to
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`% SIDTAB_SIZE` if and only if the size is a power of two (which seems
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to be always the case). One property of the binary and with a power of
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two (and probably a small one <=2048) is all higher bits are discarded.
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Thus a hash function is needed with a good avalanche effect, which the
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current one is not.
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Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
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Acked-by: James Carter <jwcart2@gmail.com>
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---
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libselinux/src/avc_sidtab.c | 17 +++++++----------
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1 file changed, 7 insertions(+), 10 deletions(-)
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diff --git a/src/avc_sidtab.c b/src/avc_sidtab.c
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index f179d855..e396a938 100644
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--- a/src/avc_sidtab.c
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+++ b/src/avc_sidtab.c
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@@ -15,16 +15,13 @@
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static inline unsigned sidtab_hash(const char * key)
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{
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- const char *p;
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- unsigned int size;
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- unsigned int val;
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-
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- val = 0;
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- size = strlen(key);
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- for (p = key; (unsigned int)(p - key) < size; p++)
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- val =
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- (val << 4 | (val >> (8 * sizeof(unsigned int) - 4))) ^ (*p);
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- return val & (SIDTAB_SIZE - 1);
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+ unsigned int hash = 5381;
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+ unsigned char c;
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+
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+ while ((c = *(unsigned const char *)key++))
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+ hash = ((hash << 5) + hash) ^ c;
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+
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+ return hash & (SIDTAB_SIZE - 1);
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}
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int sidtab_init(struct sidtab *s)
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--
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2.27.0
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