From 63f3a043dec7f0d430800ebe6361088eaca9f668 Mon Sep 17 00:00:00 2001 From: Akinobu Mita Date: Sun, 8 Dec 2024 23:24:15 +0900 Subject: [PATCH] fault-inject: use prandom where cryptographically secure randomness is not needed 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@noisy.programming.kicks-ass.net Link: https://lkml.kernel.org/r/20241208142415.205960-1-akinobu.mita@gmail.com Signed-off-by: Akinobu Mita Suggested-by: Peter Zijlstra Cc: Peter Zijlstra Cc: Masami Hiramatsu Signed-off-by: Andrew Morton --- lib/fault-inject.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/lib/fault-inject.c b/lib/fault-inject.c index 52eb6ba29698..92a54c8a8380 100644 --- a/lib/fault-inject.c +++ b/lib/fault-inject.c @@ -1,7 +1,7 @@ // SPDX-License-Identifier: GPL-2.0-only #include #include -#include +#include #include #include #include @@ -12,6 +12,24 @@ #include #include +/* + * 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 *attr, char *str) 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 *attr, ssize_t size, int flags) 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(const char *name, 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 fault_config_type = { 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);