From: Richard Cochran <richardcochran@gmail.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: davem@davemloft.net, jacob.e.keller@intel.com, netdev@vger.kernel.org
Subject: Re: [PATCH net] ptp: improve max_adj check against unreasonable values
Date: Mon, 14 Jun 2021 22:13:24 -0700 [thread overview]
Message-ID: <20210615051324.GC5517@localhost> (raw)
In-Reply-To: <20210614222405.378030-1-kuba@kernel.org>
On Mon, Jun 14, 2021 at 03:24:05PM -0700, Jakub Kicinski wrote:
> Scaled PPM conversion to PPB may (on 64bit systems) result
> in a value larger than s32 can hold (freq/scaled_ppm is a long).
> This means the kernel will not correctly reject unreasonably
> high ->freq values (e.g. > 4294967295ppb, 281474976645 scaled PPM).
>
> The conversion is equivalent to a division by ~66 (65.536),
> so the value of ppb is always smaller than ppm, but not small
> enough to assume narrowing the type from long -> s32 is okay.
>
> Note that reasonable user space (e.g. ptp4l) will not use such
> high values, anyway, 4289046510ppb ~= 4.3x, so the fix is
> somewhat pedantic.
But still important to defend against fuzzing!
> Fixes: d39a743511cd ("ptp: validate the requested frequency adjustment.")
> Fixes: d94ba80ebbea ("ptp: Added a brand new class driver for ptp clocks.")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Richard Cochran <richardcochran@gmail.com>
next prev parent reply other threads:[~2021-06-15 5:13 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-14 22:24 [PATCH net] ptp: improve max_adj check against unreasonable values Jakub Kicinski
2021-06-15 5:13 ` Richard Cochran [this message]
2021-06-15 18:10 ` patchwork-bot+netdevbpf
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