80 lines
2.5 KiB
Diff
80 lines
2.5 KiB
Diff
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From ad0958b816f28e53d9bda4486e969ec3ca63538a Mon Sep 17 00:00:00 2001
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From: Alejandro Colomar <alx@kernel.org>
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Date: Wed, 19 Jun 2024 19:54:16 +0200
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Subject: [PATCH] lib/csrand.c: Fix the lower part of the domain of
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csrand_uniform()
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I accidentally broke this code during an un-optimization. We need to
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start from a random value of the width of the limit, that is, 32 bits.
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Thanks to Jason for pointing to his similar code in the kernel, which
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made me see my mistake.
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Fixes: 2a61122b5e8f ("Unoptimize the higher part of the domain of csrand_uniform()")
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Closes: <https://github.com/shadow-maint/shadow/issues/1015>
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Reported-by: Michael Brunnbauer <https://github.com/michaelbrunnbauer>
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Link: <https://git.zx2c4.com/linux-rng/tree/drivers/char/random.c#n535>
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Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
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Link: <https://github.com/shadow-maint/shadow/pull/638>
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Link: <https://github.com/shadow-maint/shadow/issues/634>
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Link: <https://github.com/shadow-maint/shadow/pull/624>
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Tested-by: Michael Brunnbauer <https://github.com/michaelbrunnbauer>
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Reviewed-by: Michael Brunnbauer <https://github.com/michaelbrunnbauer>
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Signed-off-by: Alejandro Colomar <alx@kernel.org>
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Cherry-picked-from: 4119a2dce564 ("lib/csrand.c: Fix the lower part of the domain of csrand_uniform()")
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Cc: "Serge E. Hallyn" <serge@hallyn.com>
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Link: <https://github.com/shadow-maint/shadow/pull/1025>
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Signed-off-by: Alejandro Colomar <alx@kernel.org>
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Conflict: N/A
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Reference: https://github.com/shadow-maint/shadow/commit/ad0958b816f28e53d9bda4486e969ec3ca63538a
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---
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lib/csrand.c | 12 ++++++++++--
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1 file changed, 10 insertions(+), 2 deletions(-)
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diff --git a/lib/csrand.c b/lib/csrand.c
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index e85eaa8a..16bcccf0 100644
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--- a/lib/csrand.c
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+++ b/lib/csrand.c
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@@ -22,6 +22,7 @@
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#include "shadowlog.h"
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+static uint32_t csrand32(void);
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static uint32_t csrand_uniform32(uint32_t n);
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static unsigned long csrand_uniform_slow(unsigned long n);
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@@ -96,6 +97,13 @@ csrand_interval(unsigned long min, unsigned long max)
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}
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+static uint32_t
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+csrand32(void)
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+{
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+ return csrand();
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+}
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+
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+
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/*
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* Fast Random Integer Generation in an Interval
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* ACM Transactions on Modeling and Computer Simulation 29 (1), 2019
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@@ -108,12 +116,12 @@ csrand_uniform32(uint32_t n)
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uint64_t r, mult;
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if (n == 0)
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- return csrand();
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+ return csrand32();
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bound = -n % n; // analogous to `2^32 % n`, since `x % y == (x-y) % y`
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do {
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- r = csrand();
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+ r = csrand32();
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mult = r * n;
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rem = mult; // analogous to `mult % 2^32`
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} while (rem < bound); // p = (2^32 % n) / 2^32; W.C.: n=2^31+1, p=0.5
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--
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2.46.0
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