On 03/26/2014 06:12 PM, Sasha Levin wrote:
Commit 4af712e8df ("random32: add prandom_reseed_late() and call when
nonblocking pool becomes initialized") has added a late reseed stage
that happens as soon as the nonblocking pool is marked as initialized.
This fails in the case that the nonblocking pool gets initialized
during __prandom_reseed()'s call to get_random_bytes(). In that case
we'd double back into __prandom_reseed() in an attempt to do a late
reseed - deadlocking on 'lock' early on in the boot process.
Instead, just avoid even waiting to do a reseed if a reseed is already
occuring.
Signed-off-by: Sasha Levin <sasha.le...@oracle.com>
Thanks for catching! (If you want Dave to pick it up, please also
Cc netdev.)
Why not via spin_trylock_irqsave() ? Thus, if we already hold the
lock, we do not bother any longer with doing the same work twice
and just return.
I.e. like:
static void __prandom_reseed(bool late)
{
int i;
unsigned long flags;
static bool latch = false;
static DEFINE_SPINLOCK(lock);
/* Asking for random bytes might result in bytes getting
* moved into the nonblocking pool and thus marking it
* as initialized. In this case we would double back into
* this function and attempt to do a late reseed.
* Ignore the pointless attempt to reseed again if we're
* already waiting for bytes when the nonblocking pool
* got initialized.
*/
/* only allow initial seeding (late == false) once */
if (!spin_trylock_irqsave(&lock, flags))
return;
if (latch && !late)
goto out;
latch = true;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
u32 seeds[4];
get_random_bytes(&seeds, sizeof(seeds));
state->s1 = __seed(seeds[0], 2U);
state->s2 = __seed(seeds[1], 8U);
state->s3 = __seed(seeds[2], 16U);
state->s4 = __seed(seeds[3], 128U);
prandom_warmup(state);
}
out:
spin_unlock_irqrestore(&lock, flags);
}
---
lib/random32.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/lib/random32.c b/lib/random32.c
index 1e5b2df..b59da12 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -241,14 +241,27 @@ static void __prandom_reseed(bool late)
{
int i;
unsigned long flags;
- static bool latch = false;
+ static bool latch = false, reseeding = false;
static DEFINE_SPINLOCK(lock);
+ /*
+ * Asking for random bytes might result in bytes getting
+ * moved into the nonblocking pool and thus marking it
+ * as initialized. In this case we would double back into
+ * this function and attempt to do a late reseed.
+ * Ignore the pointless attempt to reseed again if we're
+ * already waiting for bytes when the nonblocking pool
+ * got initialized
+ */
+ if (reseeding)
+ return;
+
/* only allow initial seeding (late == false) once */
spin_lock_irqsave(&lock, flags);
if (latch && !late)
goto out;
latch = true;
+ reseeding = true;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
@@ -263,6 +276,7 @@ static void __prandom_reseed(bool late)
prandom_warmup(state);
}
out:
+ reseeding = false;
spin_unlock_irqrestore(&lock, flags);
}
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