[PATCH 4.9 043/264] random: fix soft lockup when trying to read from an uninitialized blocking pool

Greg Kroah-Hartman
2022-06-23T16:58:41Z

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;
}