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authorWilly Tarreau <w@1wt.eu>2020-07-10 15:23:19 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2020-07-29 10:35:37 -0700
commitf227e3ec3b5cad859ad15666874405e8c1bbc1d4 (patch)
tree816ed64188fc5e153f192832d89c972f1c458820
parent6ba1b005ffc388c2aeaddae20da29e4810dea298 (diff)
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>
-rw-r--r--drivers/char/random.c1
-rw-r--r--include/linux/random.h3
-rw-r--r--kernel/time/timer.c8
-rw-r--r--lib/random32.c2
4 files changed, 13 insertions, 1 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 2a41b21623ae..d20ba1b104ca 100644
--- 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 45e1f8fa742b..39aaa1f78f9d 100644
--- 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 df1ff803acc4..026ac01af9da 100644
--- 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 763b920a6206..c4d317be2997 100644
--- 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.