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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, kernel test robot <lkp@intel.com>,
        Theodore Tso <tytso@mit.edu>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>
Subject: [PATCH 4.9 043/264] random: fix soft lockup when trying to read from an uninitialized blocking pool
Date:   Thu, 23 Jun 2022 18:40:36 +0200
Message-Id: <20220623164345.287939032@linuxfoundation.org>
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From: Theodore Ts'o <tytso@mit.edu>

commit 58be0106c5306b939b07b4b8bf00669a20593f4b upstream.

Fixes: eb9d1bf079bb: "random: only read from /dev/random after its pool has received 128 bits"
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/char/random.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -774,8 +774,11 @@ retry:
 	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
 		goto retry;
 
-	if (has_initialized)
+	if (has_initialized) {
 		r->initialized = 1;
+		wake_up_interruptible(&random_read_wait);
+		kill_fasync(&fasync, SIGIO, POLL_IN);
+	}
 
 	trace_credit_entropy_bits(r->name, nbits,
 				  entropy_count >> ENTROPY_SHIFT, _RET_IP_);
@@ -791,6 +794,13 @@ retry:
 			entropy_bits = r->entropy_count >> ENTROPY_SHIFT;
 		}
 
+		/* initialize the blocking pool if necessary */
+		if (entropy_bits >= random_read_wakeup_bits &&
+		    !other->initialized) {
+			schedule_work(&other->push_work);
+			return;
+		}
+
 		/* should we wake readers? */
 		if (entropy_bits >= random_read_wakeup_bits &&
 		    wq_has_sleeper(&random_read_wait)) {
@@ -1992,8 +2002,8 @@ _random_read(int nonblock, char __user *
 			return -EAGAIN;
 
 		wait_event_interruptible(random_read_wait,
-			ENTROPY_BITS(&input_pool) >=
-			random_read_wakeup_bits);
+		    blocking_pool.initialized &&
+		    (ENTROPY_BITS(&input_pool) >= random_read_wakeup_bits));
 		if (signal_pending(current))
 			return -ERESTARTSYS;
 	}