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From:   Jann Horn <jannh@google.com>
To:     "Theodore Ts'o" <tytso@mit.edu>,
        "Jason A . Donenfeld" <Jason@zx2c4.com>
Cc:     linux-kernel@vger.kernel.org, Jann Horn <jannh@google.com>
Subject: [PATCH] random: Fix signal_pending() usage
Date:   Tue,  5 Apr 2022 18:39:31 +0200
Message-Id: <20220405163931.1108442-1-jannh@google.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

signal_pending() checks TIF_NOTIFY_SIGNAL and TIF_SIGPENDING, which signal
that the task should bail out of the syscall when possible.
This is a separate concept from need_resched(), which checks
TIF_NEED_RESCHED, signalling that the task should preempt.

In particular, with the current code, the signal_pending() bailout probably
won't work reliably.

Change this to look like other functions that read lots of data, such as
read_zero().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
---
 drivers/char/random.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1eb220a5f44f..7f0253455d4e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -540,13 +540,13 @@ static ssize_t get_random_bytes_user(void __user *buf=
, size_t nbytes)
 	crng_make_state(chacha_state, (u8 *)&chacha_state[4], CHACHA_KEY_SIZE);
=20
 	do {
-		if (large_request && need_resched()) {
+		if (large_request) {
 			if (signal_pending(current)) {
 				if (!ret)
 					ret =3D -ERESTARTSYS;
 				break;
 			}
-			schedule();
+			cond_resched();
 		}
=20
 		chacha20_block(chacha_state, output);

base-commit: 0c3e7b36d92681bba4c73c198a35e5a806d6f3ff
--=20
2.35.1.1094.g7c7d902a7c-goog