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Subject[PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5
Hi,

http://dev.gentoo.org/~pappy/kernel/linux-2.6.21.5-get_urandom_long-AT_ENTROPY.patch

this patch adds the function drivers/char/random.c:get_random_long()
and adds an AT_ENTROPY field in the auxv without config option
(the config option was removed as suggested by Arjan on LKML).

README: get_random_long() and AT_ENTROPY support for auxv
NAME: Alexander Gabert
EMAIL: pappy@gentoo.org



diff -Nru linux-2.6.21.5.ORIG/drivers/char/random.c
linux-2.6.21.5/drivers/char/random.c
--- linux-2.6.21.5.ORIG/drivers/char/random.c 2007-06-11
20:37:06.000000000 +0200
+++ linux-2.6.21.5/drivers/char/random.c 2007-06-20
17:00:35.000000000 +0200
@@ -1654,6 +1654,53 @@
}

/*
+ * get_random_long() returns a randomized unsigned long word.
+ * It recycles it's entropy cache for a given time period and
+ * uses half_md4_transform to generate a unique return value.
+ * Every REKEY_INTERVAL the cache is reloaded with fresh
+ * randomization data using get_random_bytes().
+ * This function is not intended for strong cryptographic routines.
+ */
+unsigned long get_random_long(void)
+{
+ /* remember the last time we refreshed the cache with random entropy */
+ static time_t rekey_time;
+
+ time_t t;
+
+ /*
+ * the following data in the buffer is unchanged during REKEY_INTERVAL:
+ * |----|----|KKKK|KKKK|KKKK|KKKK|KKKK|KKKK|----|----|----|----|
+ * ___0____1____2____3____4____5____6____7____8____9___10___11__
+ *
+ * the following data is updated during the first half_md4_transform call
+ * |----|YYYY|----|----|----|----|----|----|ZZZZ|ZZZZ|ZZZZ|ZZZZ|
+ * ___0____1____2____3____4____5____6____7____8____9___10___11__
+ *
+ * the following data is updated during the second half_md4_transform
+ * |XXXX|----|----|----|----|----|----|----|ZZZZ|ZZZZ|ZZZZ|ZZZZ|
+ * ___0____1____2____3____4____5____6____7____8____9___10___11__
+ */
+ static __u32 entropycache[12];
+
+ /* get the current time in seconds */
+ t = get_seconds();
+
+ /* check for REKEY_INTERVAL */
+ if (t && (!rekey_time || ((t - rekey_time) > REKEY_INTERVAL))) {
+ rekey_time = t;
+ /* refresh with random entropy */
+ get_random_bytes(entropycache, sizeof(entropycache));
+ }
+
+ /* transform the buffer to a new state, thus generating new return
value */
+ entropycache[1] = half_md4_transform(entropycache+8, entropycache);
+ entropycache[0] = half_md4_transform(entropycache+8, entropycache);
+
+ return *(unsigned long *)entropycache;
+}
+
+/*
* randomize_range() returns a start address such that
*
* [...... <range> .....]
diff -Nru linux-2.6.21.5.ORIG/fs/binfmt_elf.c linux-2.6.21.5/fs/binfmt_elf.c
--- linux-2.6.21.5.ORIG/fs/binfmt_elf.c 2007-06-11 20:37:06.000000000
+0200
+++ linux-2.6.21.5/fs/binfmt_elf.c 2007-06-20 17:02:59.000000000 +0200
@@ -201,6 +201,7 @@
NEW_AUX_ENT(AT_GID, tsk->gid);
NEW_AUX_ENT(AT_EGID, tsk->egid);
NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ NEW_AUX_ENT(AT_ENTROPY, get_random_long());
if (k_platform) {
NEW_AUX_ENT(AT_PLATFORM,
(elf_addr_t)(unsigned long)u_platform);
diff -Nru linux-2.6.21.5.ORIG/include/linux/auxvec.h
linux-2.6.21.5/include/linux/auxvec.h
--- linux-2.6.21.5.ORIG/include/linux/auxvec.h 2007-06-11
20:37:06.000000000 +0200
+++ linux-2.6.21.5/include/linux/auxvec.h 2007-06-20
16:47:44.000000000 +0200
@@ -26,6 +26,8 @@

#define AT_SECURE 23 /* secure mode boolean */

-#define AT_VECTOR_SIZE 44 /* Size of auxiliary table. */
+#define AT_ENTROPY 24 /* kernel entropy in auxv */
+
+#define AT_VECTOR_SIZE 45 /* Size of auxiliary table in. */

#endif /* _LINUX_AUXVEC_H */
diff -Nru linux-2.6.21.5.ORIG/include/linux/random.h
linux-2.6.21.5/include/linux/random.h
--- linux-2.6.21.5.ORIG/include/linux/random.h 2007-06-11
20:37:06.000000000 +0200
+++ linux-2.6.21.5/include/linux/random.h 2007-06-20
16:19:02.000000000 +0200
@@ -67,6 +67,9 @@
#endif

unsigned int get_random_int(void);
+
+unsigned long get_random_long(void);
+
unsigned long randomize_range(unsigned long start, unsigned long end,
unsigned long len);

u32 random32(void);


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