Commit d06bfd19 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Theodore Ts'o
Browse files

random: warn when kernel uses unseeded randomness 



This enables an important dmesg notification about when drivers have
used the crng without it being seeded first. Prior, these errors would
occur silently, and so there hasn't been a great way of diagnosing these
types of bugs for obscure setups. By adding this as a config option, we
can leave it on by default, so that we learn where these issues happen,
in the field, will still allowing some people to turn it off, if they
really know what they're doing and do not want the log entries.

However, we don't leave it _completely_ by default. An earlier version
of this patch simply had `default y`. I'd really love that, but it turns
out, this problem with unseeded randomness being used is really quite
present and is going to take a long time to fix. Thus, as a compromise
between log-messages-for-all and nobody-knows, this is `default y`,
except it is also `depends on DEBUG_KERNEL`. This will ensure that the
curious see the messages while others don't have to.

Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 7aed9f72

drivers/char/random.c

+13 −2
Original line number Original line Diff line number Diff line
@@ -288,7 +288,6 @@ 
#define SEC_XFER_SIZE		512

#define SEC_XFER_SIZE		512

#define EXTRACT_SIZE		10

#define EXTRACT_SIZE		10





#define DEBUG_RANDOM_BOOT 0





#define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))

#define LONGS(x) (((x) + sizeof(unsigned long) - 1)/sizeof(unsigned long))
@@ -1481,7 +1480,7 @@ void get_random_bytes(void *buf, int nbytes) 
{

{

	__u8 tmp[CHACHA20_BLOCK_SIZE];

	__u8 tmp[CHACHA20_BLOCK_SIZE];





#if DEBUG_RANDOM_BOOT > 0

#ifdef CONFIG_WARN_UNSEEDED_RANDOM

	if (!crng_ready())

	if (!crng_ready())

		printk(KERN_NOTICE "random: %pF get_random_bytes called "

		printk(KERN_NOTICE "random: %pF get_random_bytes called "

		       "with crng_init = %d\n", (void *) _RET_IP_, crng_init);

		       "with crng_init = %d\n", (void *) _RET_IP_, crng_init);
@@ -2075,6 +2074,12 @@ u64 get_random_u64(void) 
	    return ret;

	    return ret;

#endif

#endif





#ifdef CONFIG_WARN_UNSEEDED_RANDOM

	if (!crng_ready())

		printk(KERN_NOTICE "random: %pF get_random_u64 called "

		       "with crng_init = %d\n", (void *) _RET_IP_, crng_init);

#endif



	batch = &get_cpu_var(batched_entropy_u64);

	batch = &get_cpu_var(batched_entropy_u64);

	if (use_lock)

	if (use_lock)

		read_lock_irqsave(&batched_entropy_reset_lock, flags);

		read_lock_irqsave(&batched_entropy_reset_lock, flags);
@@ -2101,6 +2106,12 @@ u32 get_random_u32(void) 
	if (arch_get_random_int(&ret))

	if (arch_get_random_int(&ret))

		return ret;

		return ret;





#ifdef CONFIG_WARN_UNSEEDED_RANDOM

	if (!crng_ready())

		printk(KERN_NOTICE "random: %pF get_random_u32 called "

		       "with crng_init = %d\n", (void *) _RET_IP_, crng_init);

#endif



	batch = &get_cpu_var(batched_entropy_u32);

	batch = &get_cpu_var(batched_entropy_u32);

	if (use_lock)

	if (use_lock)

		read_lock_irqsave(&batched_entropy_reset_lock, flags);

		read_lock_irqsave(&batched_entropy_reset_lock, flags);

lib/Kconfig.debug

+16 −0
Original line number Original line Diff line number Diff line
@@ -1209,6 +1209,22 @@ config STACKTRACE 
	  It is also used by various kernel debugging features that require

	  It is also used by various kernel debugging features that require

	  stack trace generation.

	  stack trace generation.





config WARN_UNSEEDED_RANDOM

	bool "Warn when kernel uses unseeded randomness"

	default y

	depends on DEBUG_KERNEL

	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.



	  Say Y here, unless you simply do not care about using unseeded

	  randomness and do not want a potential warning message in your logs.



config DEBUG_KOBJECT

config DEBUG_KOBJECT

	bool "kobject debugging"

	bool "kobject debugging"

	depends on DEBUG_KERNEL

	depends on DEBUG_KERNEL

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