linux-kernel - [PATCH 4/6] selinux: simplify avtab slot calculation

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Message-Id: <20230818151220.166215-3-cgzones@googlemail.com>
Date:   Fri, 18 Aug 2023 17:12:15 +0200
From:   Christian Göttsche <cgzones@...glemail.com>
To:     selinux@...r.kernel.org
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] selinux: simplify avtab slot calculation

Instead of dividing by 8 and then performing log2 by hand, use a more
readable calculation.

The behavior of rounddown_pow_of_two() for an input of 0 is undefined,
so handle that case and small values manually to achieve the same
results.

Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
---
 security/selinux/ss/avtab.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/security/selinux/ss/avtab.c b/security/selinux/ss/avtab.c
index 955cfe495606..1d1ffe085b35 100644
--- a/security/selinux/ss/avtab.c
+++ b/security/selinux/ss/avtab.c
@@ -298,13 +298,7 @@ int avtab_alloc(struct avtab *h, u32 nrules)
 	u32 nslot = 0;
 
 	if (nrules != 0) {
-		u32 shift = 1;
-		u32 work = nrules >> 3;
-		while (work) {
-			work >>= 1;
-			shift++;
-		}
-		nslot = 1 << shift;
+		nslot = nrules > 3 ? rounddown_pow_of_two(nrules / 2) : 2;
 		if (nslot > MAX_AVTAB_HASH_BUCKETS)
 			nslot = MAX_AVTAB_HASH_BUCKETS;
 
-- 
2.40.1