random32: update the net random state on interrupt and activity

This modifies the first 32 bits out of the 128 bits of a random CPU's
net_rand_state on interrupt or CPU activity to complicate remote
observations that could lead to guessing the network RNG's internal
state.

Note that depending on some network devices' interrupt rate moderation
or binding, this re-seeding might happen on every packet or even almost
never.

In addition, with NOHZ some CPUs might not even get timer interrupts,
leaving their local state rarely updated, while they are running
networked processes making use of the random state.  For this reason, we
also perform this update in update_process_times() in order to at least
update the state when there is user or system activity, since it's the
only case we care about.

Reported-by: Amit Klein <aksecurity@gmail.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 2a41b21623ae42b6efdf530287c5f7e20660e3a1..d20ba1b104ca3aceadd19fb6fbcb9ba035799a62 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1277,6 +1277,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
 
        fast_mix(fast_pool);
        add_interrupt_bench(cycles);
+       this_cpu_add(net_rand_state.s1, fast_pool->pool[cycles & 3]);
 
        if (unlikely(crng_init == 0)) {
                if ((fast_pool->count >= 64) &&

diff --git a/include/linux/random.h b/include/linux/random.h
index 45e1f8fa742bcdaec079e7e64999ece155f01385..39aaa1f78f9ddeb26058a1147157c5b4e03f31e6 100644 (file)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -11,6 +11,7 @@
 #include <linux/kernel.h>
 #include <linux/list.h>
 #include <linux/once.h>
+#include <linux/percpu.h>
 
 #include <uapi/linux/random.h>
 
@@ -119,6 +120,8 @@ struct rnd_state {
        __u32 s1, s2, s3, s4;
 };
 
+DECLARE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;
+
 u32 prandom_u32_state(struct rnd_state *state);
 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index df1ff803acc4ff1338c535b58e2b78e160a8d308..026ac01af9da7e7619ec365e1efbdd638c0b2695 100644 (file)
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -43,6 +43,7 @@
 #include <linux/sched/debug.h>
 #include <linux/slab.h>
 #include <linux/compat.h>
+#include <linux/random.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -1742,6 +1743,13 @@ void update_process_times(int user_tick)
        scheduler_tick();
        if (IS_ENABLED(CONFIG_POSIX_TIMERS))
                run_posix_cpu_timers();
+
+       /* The current CPU might make use of net randoms without receiving IRQs
+        * to renew them often enough. Let's update the net_rand_state from a
+        * non-constant value that's not affine to the number of calls to make
+        * sure it's updated when there's some activity (we don't care in idle).
+        */
+       this_cpu_add(net_rand_state.s1, rol32(jiffies, 24) + user_tick);
 }
 
 /**

diff --git a/lib/random32.c b/lib/random32.c
index 763b920a6206cd6ffc4cd9668885223f2d6a2790..c4d317be2997b5096b9cd68b281726a23c368323 100644 (file)
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -48,7 +48,7 @@ static inline void prandom_state_selftest(void)
 }
 #endif
 
-static DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;
+DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;
 
 /**
  *     prandom_u32_state - seeded pseudo-random number generator.