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

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Message-ID: <f4dc15ff-10cf-bb73-5f72-874dd2b85f1a@w6rz.net>
Date:   Thu, 16 Jun 2022 19:10:36 -0700
From:   Ron Economos <re@...z.net>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH] random: quiet urandom warning ratelimit suppression
 message

On 6/16/22 6:20 AM, Jason A. Donenfeld wrote:
> 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)
>   

Tested on 5.15.48 kernel for RISC-V RV64. Works good, urandom_read_iter 
warnings are suppressed.

Tested-by: Ron Economos <re@...z.net>