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Message-ID: <20240229225910.79e224cf@kernel.org>
Date: Thu, 29 Feb 2024 22:59:10 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
<edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com>, "Gustavo A. R. Silva"
<gustavoars@...nel.org>, netdev@...r.kernel.org,
linux-hardening@...r.kernel.org, Simon Horman <horms@...nel.org>, Jiri
Pirko <jiri@...nulli.us>, Daniel Borkmann <daniel@...earbox.net>, Coco Li
<lixiaoyan@...gle.com>, Amritha Nambiar <amritha.nambiar@...el.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netdev: Use flexible array for trailing private bytes
On Thu, 29 Feb 2024 13:30:22 -0800 Kees Cook wrote:
> Introduce a new struct net_device_priv that contains struct net_device
> but also accounts for the commonly trailing bytes through the "size" and
> "data" members.
I'm a bit unclear on the benefit. Perhaps I'm unaccustomed to "safe C".
> As many dummy struct net_device instances exist still,
> it is non-trivial to but this flexible array inside struct net_device
put
Non-trivial, meaning what's the challenge?
We also do somewhat silly things with netdev lifetime, because we can't
assume netdev gets freed by netdev_free(). Cleaning up the "embedders"
would be beneficial for multiple reasons.
> itself. But we can add a sanity check in netdev_priv() to catch any
> attempts to access the private data of a dummy struct.
>
> Adjust allocation logic to use the new full structure.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 118c40258d07..b476809d0bae 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1815,6 +1815,8 @@ enum netdev_stat_type {
> NETDEV_PCPU_STAT_DSTATS, /* struct pcpu_dstats */
> };
>
> +#define NETDEV_ALIGN 32
Unless someone knows what this is for it should go.
Align priv to cacheline size.
> /**
> * struct net_device - The DEVICE structure.
> *
> @@ -2665,7 +2673,14 @@ void dev_net_set(struct net_device *dev, struct net *net)
> */
> static inline void *netdev_priv(const struct net_device *dev)
> {
> - return (char *)dev + ALIGN(sizeof(struct net_device), NETDEV_ALIGN);
> + struct net_device_priv *priv;
> +
> + /* Dummy struct net_device have no trailing data. */
> + if (WARN_ON_ONCE(dev->reg_state == NETREG_DUMMY))
> + return NULL;
This is a static inline with roughly 11,000 call sites, according to
a quick grep. Aren't WARN_ONCE() in static inlines creating a "once"
object in every compilation unit where they get used?
> + priv = container_of(dev, struct net_device_priv, dev);
> + return (u8 *)priv->data;
> }
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