Date: Sun, 2 Feb 2003 15:30:35 +0300 From: "Andrey A. Chernov" <ache@nagual.pp.ru> To: Kris Kennaway <kris@obsecurity.org> Cc: current@FreeBSD.ORG Subject: Re: rand() is broken Message-ID: <20030202123035.GB62977@nagual.pp.ru> In-Reply-To: <20030202102621.GA60900@nagual.pp.ru> References: <20030202070644.GA9987@rot13.obsecurity.org> <20030202090422.GA59750@nagual.pp.ru> <20030202091106.GA72723@rot13.obsecurity.org> <20030202102621.GA60900@nagual.pp.ru>
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[-- Attachment #1 --]
On Sun, Feb 02, 2003 at 13:26:21 +0300, Andrey A. Chernov wrote:
> Workaround I find so far is something like that
>
> #define MASK 123459876
I found nothing better. Here is fix for 0 problem I plan to commit:
--- stdlib/rand.c.old Sat Jan 4 20:39:19 2003
+++ stdlib/rand.c Sun Feb 2 14:43:42 2003
@@ -70,14 +70,18 @@
* Park and Miller, Communications of the ACM, vol. 31, no. 10,
* October 1988, p. 1195.
*/
+#define SHIFT_MASK 123459876
long hi, lo, x;
- hi = *ctx / 127773;
- lo = *ctx % 127773;
+ /* Can't be initialized with 0, so use shifting mask. */
+ x = *ctx ^ SHIFT_MASK;
+ hi = x / 127773;
+ lo = x % 127773;
x = 16807 * lo - 2836 * hi;
- if (x <= 0)
+ if (x < 0)
x += 0x7fffffff;
- return ((*ctx = x) % ((u_long)RAND_MAX + 1));
+ *ctx = x ^ SHIFT_MASK;
+ return (x % ((u_long)RAND_MAX + 1));
#endif /* !USE_WEAK_SEEDING */
}
@@ -86,8 +90,10 @@
rand_r(unsigned int *ctx)
{
u_long val = (u_long) *ctx;
- *ctx = do_rand(&val);
- return (int) *ctx;
+ int r = do_rand(&val);
+
+ *ctx = (unsigned int) val;
+ return (r);
}
--- stdlib/random.c.old Sun Mar 24 23:42:48 2002
+++ stdlib/random.c Sun Feb 2 15:24:38 2003
@@ -142,6 +142,10 @@
*/
#define MAX_TYPES 5 /* max number of types above */
+#ifndef USE_WEAK_SEEDING
+#define SHIFT_MASK 123459876
+#endif
+
static long degrees[MAX_TYPES] = { DEG_0, DEG_1, DEG_2, DEG_3, DEG_4 };
static long seps [MAX_TYPES] = { SEP_0, SEP_1, SEP_2, SEP_3, SEP_4 };
@@ -171,12 +175,12 @@
0x36413f93, 0xc622c298, 0xf5a42ab8, 0x8a88d77b, 0xf5ad9d0e, 0x8999220b,
0x27fb47b9,
#else /* !USE_WEAK_SEEDING */
- 0x991539b1, 0x16a5bce3, 0x6774a4cd, 0x3e01511e, 0x4e508aaa, 0x61048c05,
- 0xf5500617, 0x846b7115, 0x6a19892c, 0x896a97af, 0xdb48f936, 0x14898454,
- 0x37ffd106, 0xb58bff9c, 0x59e17104, 0xcf918a49, 0x09378c83, 0x52c7a471,
- 0x8d293ea9, 0x1f4fc301, 0xc3db71be, 0x39b44e1c, 0xf8a44ef9, 0x4c8b80b1,
- 0x19edc328, 0x87bf4bdd, 0xc9b240e5, 0xe9ee4b1b, 0x4382aee7, 0x535b6b41,
- 0xf3bec5da
+ 0x52a59789, 0x43164b1c, 0x7be52a82, 0x748ef343, 0x642a8923, 0x6ade1cd8,
+ 0x1ae76e27, 0x24b915ee, 0x2c42f326, 0x12ab3ee1, 0x4679af03, 0x876d19a0,
+ 0xe9e535ba, 0xad2471c8, 0x710262f8, 0xe1c16494, 0x29224bcc, 0x9710c348,
+ 0x7347f8e4, 0xe01ef1b4, 0x2030c33f, 0xd465e38, 0x925375aa, 0x6091d15d,
+ 0x467ee7d7, 0x92713312, 0x32346127, 0x8350e834, 0x3dadc6ea, 0x391364f2,
+ 0x8226561c,
#endif /* !USE_WEAK_SEEDING */
};
@@ -236,12 +240,14 @@
*/
long hi, lo;
+ /* Can't be initialized with 0, so use shifting mask. */
+ x ^= SHIFT_MASK;
hi = x / 127773;
lo = x % 127773;
x = 16807 * lo - 2836 * hi;
- if (x <= 0)
+ if (x < 0)
x += 0x7fffffff;
- return (x);
+ return (x ^ SHIFT_MASK); /* return state, not value */
#endif /* !USE_WEAK_SEEDING */
}
@@ -473,7 +479,12 @@
if (rand_type == TYPE_0) {
i = state[0];
- state[0] = i = (good_rand(i)) & 0x7fffffff;
+ state[0] = good_rand(i);
+#ifndef USE_WEAK_SEEDING
+ i = state[0] ^ SHIFT_MASK;
+#else
+ i = state[0] & 0x7fffffff;
+#endif
} else {
/*
* Use local variables rather than static variables for speed.
--
Andrey A. Chernov
http://ache.pp.ru/
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