From: "Jason A. Donenfeld" Subject: [PATCH RFC 1/3] random: add synchronous API for the urandom pool Date: Sat, 3 Jun 2017 04:32:02 +0200 Message-ID: <20170603023204.30933-2-Jason@zx2c4.com> References: <20170603023204.30933-1-Jason@zx2c4.com> Cc: "Jason A. Donenfeld" To: Theodore Ts'o , Linux Crypto Mailing List , LKML , kernel-hardening@lists.openwall.com Return-path: Received: from frisell.zx2c4.com ([192.95.5.64]:57039 "EHLO frisell.zx2c4.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751142AbdFCCcU (ORCPT ); Fri, 2 Jun 2017 22:32:20 -0400 In-Reply-To: <20170603023204.30933-1-Jason@zx2c4.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: This enables users of get_random_{bytes,u32,u64,int,long} to wait until the pool is ready before using this function, in case they actually want to have reliable randomness. Signed-off-by: Jason A. Donenfeld --- drivers/char/random.c | 46 ++++++++++++++++++++++++++++++++++++++++++++-- include/linux/random.h | 1 + 2 files changed, 45 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 0ab024918907..bee7b1349bcb 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1466,7 +1466,10 @@ static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf, * number of good random numbers, suitable for key generation, seeding * TCP sequence numbers, etc. It does not rely on the hardware random * number generator. For random bytes direct from the hardware RNG - * (when available), use get_random_bytes_arch(). + * (when available), use get_random_bytes_arch(). In order to ensure + * that the randomness provided by this function is okay, the function + * wait_for_random_bytes() should be called and return 0 at least once + * at any point prior. */ void get_random_bytes(void *buf, int nbytes) { @@ -1496,6 +1499,42 @@ void get_random_bytes(void *buf, int nbytes) EXPORT_SYMBOL(get_random_bytes); /* + * Wait for the urandom pool to be seeded and thus guaranteed to supply + * cryptographically secure random numbers. This applies to: the /dev/urandom + * device, the get_random_bytes function, and the get_random_{u32,u64,int,long} + * family of functions. Using any of these functions without first calling + * this function forfeits the guarantee of security. + * + * If is_interruptable is true, then this uses wait_event_interruptable. + * Otherwise the calling process will not respond to signals. If timeout is + * 0, then, unless interrupted, this function will wait potentially forever. + * Otherwise, timeout is a measure in jiffies. + * + * Returns: 0 if the urandom pool has been seeded. + * -ERESTARTSYS if the function was interrupted or timed out. + * Other return values of the wait_event_* functions. + */ +int wait_for_random_bytes(bool is_interruptable, unsigned long timeout) +{ + if (likely(crng_ready())) + return 0; + if (is_interruptable && timeout) + return wait_event_interruptible_timeout(crng_init_wait, crng_ready(), timeout); + if (is_interruptable && !timeout) + return wait_event_interruptible(crng_init_wait, crng_ready()); + if (!is_interruptable && timeout) + return wait_event_timeout(crng_init_wait, crng_ready(), timeout); + if (!is_interruptable && !timeout) { + wait_event(crng_init_wait, crng_ready()); + return 0; + } + + BUG(); /* This BUG() should be compiled out as unreachable code, but just in case... */ + return -EINVAL; +} +EXPORT_SYMBOL(wait_for_random_bytes); + +/* * Add a callback function that will be invoked when the nonblocking * pool is initialised. * @@ -2023,7 +2062,10 @@ struct batched_entropy { /* * Get a random word for internal kernel use only. The quality of the random * number is either as good as RDRAND or as good as /dev/urandom, with the - * goal of being quite fast and not depleting entropy. + * goal of being quite fast and not depleting entropy. In order to ensure + * that the randomness provided by this function is okay, the function + * wait_for_random_bytes() should be called and return 0 at least once + * at any point prior. */ static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64); u64 get_random_u64(void) diff --git a/include/linux/random.h b/include/linux/random.h index ed5c3838780d..20dd73418bd5 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -34,6 +34,7 @@ extern void add_input_randomness(unsigned int type, unsigned int code, extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy; extern void get_random_bytes(void *buf, int nbytes); +extern int wait_for_random_bytes(bool is_interruptable, unsigned long timeout); extern int add_random_ready_callback(struct random_ready_callback *rdy); extern void del_random_ready_callback(struct random_ready_callback *rdy); extern void get_random_bytes_arch(void *buf, int nbytes); -- 2.13.0