From: Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> Cc: "Theodore Ts'o" <tytso@xxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jessica Yu <jeyu@xxxxxxxxxx> Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Prarit Bhargava <prarit@xxxxxxxxxx> Cc: Lokesh Vutla <lokeshvutla@xxxxxx> Cc: Nicholas Piggin <npiggin@xxxxxxxxx> Cc: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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();
