[PATCH 4.9 013/264] random: do not ignore early device randomness

Greg Kroah-Hartman
2022-06-23T16:45:58Z

From: Kees Cook <keescook@chromium.org>

commit ee7998c50c2697737c6530431709f77c852bf0d6 upstream.

The add_device_randomness() function would ignore incoming bytes if the
crng wasn't ready. This additionally makes sure to make an early enough
call to add_latent_entropy() to influence the initial stack canary,
which is especially important on non-x86 systems where it stays the same
through the life of the boot.

Link: http://lkml.kernel.org/r/20170626233038.GA48751@beast
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jessica Yu <jeyu@redhat.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 5 +++++
init/main.c | 1 +
2 files changed, 6 insertions(+)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1045,6 +1045,11 @@ void add_device_randomness(const void *b
unsigned long time = random_get_entropy() ^ jiffies;
unsigned long flags;

+ if (!crng_ready()) {
+ crng_fast_load(buf, size);
+ return;
+ }
+
trace_add_device_randomness(size, _RET_IP_);
spin_lock_irqsave(&input_pool.lock, flags);
_mix_pool_bytes(&input_pool, buf, size);
--- a/init/main.c
+++ b/init/main.c
@@ -490,6 +490,7 @@ asmlinkage __visible void __init start_k
/*
* Set up the the initial canary ASAP:
*/
+ add_latent_entropy();
boot_init_stack_canary();

cgroup_init_early();