The patch titled
Subject: fault-inject: use prandom where cryptographically secure randomness is not needed
has been added to the -mm mm-nonmm-unstable branch. Its filename is
fault-inject-use-prandom-where-cryptographically-secure-randomness-is-not-needed.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fault-inject-use-prandom-where-cryptographically-secure-randomness-is-not-needed.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Subject: fault-inject: use prandom where cryptographically secure randomness is not needed
Date: Sun, 8 Dec 2024 23:24:15 +0900
Currently get_random*() is used to determine the probability of fault
injection, but cryptographically secure random numbers are not required.
There is no big problem in using prandom instead of get_random*() to
determine the probability of fault injection, and it also avoids acquiring
a spinlock, which is unsafe in some contexts.
Link: https://lore.kernel.org/lkml/20241129120939.GG35539@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20241208142415.205960-1-akinobu.mita@xxxxxxxxx
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/fault-inject.c | 28 ++++++++++++++++++++++++++--
1 file changed, 26 insertions(+), 2 deletions(-)
--- a/lib/fault-inject.c~fault-inject-use-prandom-where-cryptographically-secure-randomness-is-not-needed
+++ a/lib/fault-inject.c
@@ -1,7 +1,7 @@
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/kernel.h>
#include <linux/init.h>
-#include <linux/random.h>
+#include <linux/prandom.h>
#include <linux/debugfs.h>
#include <linux/sched.h>
#include <linux/stat.h>
@@ -13,6 +13,24 @@
#include <linux/fault-inject.h>
/*
+ * The should_fail() use prandom instead of the normal Linux RNG since they don't
+ * need cryptographically secure random numbers.
+ */
+static DEFINE_PER_CPU(struct rnd_state, fault_rnd_state);
+
+static u32 fault_prandom_u32_below_100(void)
+{
+ struct rnd_state *state;
+ u32 res;
+
+ state = &get_cpu_var(fault_rnd_state);
+ res = prandom_u32_state(state);
+ put_cpu_var(fault_rnd_state);
+
+ return res % 100;
+}
+
+/*
* setup_fault_attr() is a helper function for various __setup handlers, so it
* returns 0 on error, because that is what __setup handlers do.
*/
@@ -31,6 +49,8 @@ int setup_fault_attr(struct fault_attr *
return 0;
}
+ prandom_init_once(&fault_rnd_state);
+
attr->probability = probability;
attr->interval = interval;
atomic_set(&attr->times, times);
@@ -146,7 +166,7 @@ bool should_fail_ex(struct fault_attr *a
return false;
}
- if (attr->probability <= get_random_u32_below(100))
+ if (attr->probability <= fault_prandom_u32_below_100())
return false;
fail:
@@ -219,6 +239,8 @@ struct dentry *fault_create_debugfs_attr
if (IS_ERR(dir))
return dir;
+ prandom_init_once(&fault_rnd_state);
+
debugfs_create_ul("probability", mode, dir, &attr->probability);
debugfs_create_ul("interval", mode, dir, &attr->interval);
debugfs_create_atomic_t("times", mode, dir, &attr->times);
@@ -431,6 +453,8 @@ static const struct config_item_type fau
void fault_config_init(struct fault_config *config, const char *name)
{
+ prandom_init_once(&fault_rnd_state);
+
config_group_init_type_name(&config->group, name, &fault_config_type);
}
EXPORT_SYMBOL_GPL(fault_config_init);
_
Patches currently in -mm which might be from akinobu.mita@xxxxxxxxx are
fault-inject-use-prandom-where-cryptographically-secure-randomness-is-not-needed.patch
