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Message-ID: <20240227075605.18ec70b8@kernel.org>
Date: Tue, 27 Feb 2024 07:56:05 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Donald Hunter <donald.hunter@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
pabeni@...hat.com, jiri@...nulli.us, sdf@...gle.com,
nicolas.dichtel@...nd.com
Subject: Re: [PATCH net-next 00/15] tools: ynl: stop using libmnl
On Tue, 27 Feb 2024 10:49:42 +0000 Donald Hunter wrote:
> > +static inline bool
> > +__ynl_attr_put_overflow(struct nlmsghdr *nlh, size_t size)
> > +{
> > + bool o;
> > +
> > + /* We stash buffer length on nlmsg_pid. */
> > + o = nlh->nlmsg_len + NLA_HDRLEN + NLMSG_ALIGN(size) > nlh->nlmsg_pid;
>
> The comment confused me here. How about "We compare against stashed buffer
> length in nlmsg_pid".
The comment should give context, rather than describe the code so how
about:
/* ynl_msg_start() stashed buffer length in nlmsg_pid. */
> > + if (o)
> > + nlh->nlmsg_pid = YNL_MSG_OVERFLOW;
>
> It took me a moment to realise that this behaves like a very short
> buffer length for subsequent calls to __ynl_attr_put_overflow(). Is it
> worth extending the comment in ynl_msg_start() to say "buffer length or
> overflow status"?
Added:
/* YNL_MSG_OVERFLOW is < NLMSG_HDRLEN, all subsequent checks
* are guaranteed to fail.
*/
SG?
> > + return o;
> > +}
> > +
> > static inline struct nlattr *
> > ynl_attr_nest_start(struct nlmsghdr *nlh, unsigned int attr_type)
> > {
> > struct nlattr *attr;
> >
> > + if (__ynl_attr_put_overflow(nlh, 0))
> > + return ynl_nlmsg_end_addr(nlh) - NLA_HDRLEN;
>
> Is the idea here to return a struct nlattr * that is safe to use?
> Shouldn't we zero the values in the buffer first?
The only thing that the attr is used for is to call ynl_attr_nest_end().
so I think zero init won't make any difference.
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