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: 4af712e8df99 ("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>

1 files changed, 12 insertions, 1 deletions

diff --git a/lib/random32.c b/lib/random32.c
index 1e5b2df44291..614896778700 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -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;