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random32: avoid attempt to late reseed if in the middle of seeding 

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.

Fixes: 4af712e8df ("random32: add prandom_reseed_late() and call when nonblocking pool becomes initialized")
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Sasha Levin 2014-03-28 17:38:42 +01:00 committed by David S. Miller
parent 335a67d2ad
commit 05efa8c943
1 changed files with 12 additions and 1 deletions
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13
lib/random32.c
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@ -244,8 +244,19 @@ static void __prandom_reseed(bool late)
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 */
spin_lock_irqsave(&lock, flags);
if (!spin_trylock_irqsave(&lock, flags))
return;
if (latch && !late)
goto out;
latch = true;