Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull random updates from Ted Ts'o:
 "Add wait_for_random_bytes() and get_random_*_wait() functions so that
  callers can more safely get random bytes if they can block until the
  CRNG is initialized.

  Also print a warning if get_random_*() is called before the CRNG is
  initialized. By default, only one single-line warning will be printed
  per boot. If CONFIG_WARN_ALL_UNSEEDED_RANDOM is defined, then a
  warning will be printed for each function which tries to get random
  bytes before the CRNG is initialized. This can get spammy for certain
  architecture types, so it is not enabled by default"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: reorder READ_ONCE() in get_random_uXX
  random: suppress spammy warnings about unseeded randomness
  random: warn when kernel uses unseeded randomness
  net/route: use get_random_int for random counter
  net/neighbor: use get_random_u32 for 32-bit hash random
  rhashtable: use get_random_u32 for hash_rnd
  ceph: ensure RNG is seeded before using
  iscsi: ensure RNG is seeded before use
  cifs: use get_random_u32 for 32-bit lock random
  random: add get_random_{bytes,u32,u64,int,long,once}_wait family
  random: add wait_for_random_bytes() API

lib/Kconfig.debug

@@ -1223,6 +1223,34 @@ config STACKTRACE
 	  It is also used by various kernel debugging features that require
 	  stack trace generation.
 
+config WARN_ALL_UNSEEDED_RANDOM
+	bool "Warn for all uses of unseeded randomness"
+	default n
+	help
+	  Some parts of the kernel contain bugs relating to their use of
+	  cryptographically secure random numbers before it's actually possible
+	  to generate those numbers securely. This setting ensures that these
+	  flaws don't go unnoticed, by enabling a message, should this ever
+	  occur. This will allow people with obscure setups to know when things
+	  are going wrong, so that they might contact developers about fixing
+	  it.
+
+	  Unfortunately, on some models of some architectures getting
+	  a fully seeded CRNG is extremely difficult, and so this can
+	  result in dmesg getting spammed for a surprisingly long
+	  time.  This is really bad from a security perspective, and
+	  so architecture maintainers really need to do what they can
+	  to get the CRNG seeded sooner after the system is booted.
+	  However, since users can not do anything actionble to
+	  address this, by default the kernel will issue only a single
+	  warning for the first use of unseeded randomness.
+
+	  Say Y here if you want to receive warnings for all uses of
+	  unseeded randomness.  This will be of use primarily for
+	  those developers interersted in improving the security of
+	  Linux kernels running on their architecture (or
+	  subarchitecture).
+
 config DEBUG_KOBJECT
 	bool "kobject debugging"
 	depends on DEBUG_KERNEL

lib/rhashtable.c

@@ -234,7 +234,7 @@ static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 
 	INIT_LIST_HEAD(&tbl->walkers);
 
-	get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
+	tbl->hash_rnd = get_random_u32();
 
 	for (i = 0; i < nbuckets; i++)
 		INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);