Messages in this thread | | | Date | Thu, 29 Feb 2024 22:59:10 -0800 | From | Jakub Kicinski <> | Subject | Re: [PATCH] netdev: Use flexible array for trailing private bytes |
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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@chromium.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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