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    Subject[PATCH 4.9 013/264] random: do not ignore early device randomness
    Date
    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();

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