linux-kernel - [PATCH] random: quiet urandom warning ratelimit suppression message

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Message-Id: <20220616132029.443033-1-Jason@zx2c4.com>
Date:   Thu, 16 Jun 2022 15:20:29 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>, stable@...r.kernel.org,
        Jon Hunter <jonathanh@...dia.com>, Ron Economos <re@...z.net>
Subject: [PATCH] random: quiet urandom warning ratelimit suppression message

random.c ratelimits how much it warns about uninitialized urandom reads
using __ratelimit. When the RNG is finally initialized, it prints the
number of missed messages due to ratelimiting.

It has been this way since that functionality was introduced back in
2018. Recently, cc1e127bfa95 ("random: remove ratelimiting for in-kernel
unseeded randomness") put a bit more stress on the urandom ratelimiting,
which teased out a bug in the implementation.

Specifically, when under pressure, __ratelimit() will print its own
message and reset the count back to 0, making the final message at the
end less useful. Secondly, it does so as a pr_warn(), which apparently
is undesirable for people's CI.

Fortunately, __ratelimit() has the RATELIMIT_MSG_ON_RELEASE flag exactly
for this purpose, so we set the flag.

Fixes: 4e00b339e264 ("random: rate limit unseeded randomness warnings")
Cc: stable@...r.kernel.org
Reported-by: Jon Hunter <jonathanh@...dia.com>
Reported-by: Ron Economos <re@...z.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/char/random.c           |  2 +-
 include/linux/ratelimit_types.h | 12 ++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d0e4c89c4fcb..07a022e24057 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -87,7 +87,7 @@ static struct fasync_struct *fasync;
 
 /* Control how we warn userspace. */
 static struct ratelimit_state urandom_warning =
-	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
+	RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
 static int ratelimit_disable __read_mostly =
 	IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
diff --git a/include/linux/ratelimit_types.h b/include/linux/ratelimit_types.h
index c21c7f8103e2..002266693e50 100644
--- a/include/linux/ratelimit_types.h
+++ b/include/linux/ratelimit_types.h
@@ -23,12 +23,16 @@ struct ratelimit_state {
 	unsigned long	flags;
 };
 
-#define RATELIMIT_STATE_INIT(name, interval_init, burst_init) {		\
-		.lock		= __RAW_SPIN_LOCK_UNLOCKED(name.lock),	\
-		.interval	= interval_init,			\
-		.burst		= burst_init,				\
+#define RATELIMIT_STATE_INIT_FLAGS(name, interval_init, burst_init, flags_init) { \
+		.lock		= __RAW_SPIN_LOCK_UNLOCKED(name.lock),		  \
+		.interval	= interval_init,				  \
+		.burst		= burst_init,					  \
+		.flags		= flags_init,					  \
 	}
 
+#define RATELIMIT_STATE_INIT(name, interval_init, burst_init) \
+	RATELIMIT_STATE_INIT_FLAGS(name, interval_init, burst_init, 0)
+
 #define RATELIMIT_STATE_INIT_DISABLED					\
 	RATELIMIT_STATE_INIT(ratelimit_state, 0, DEFAULT_RATELIMIT_BURST)
 
-- 
2.35.1