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SubjectRe: [RFC 1/5] net: rtnetlink: Fix incorrect RCU API usage
On Tue, Feb 19, 2019 at 11:08:23PM -0500, Joel Fernandes (Google) wrote:
> From: Joel Fernandes <joel@joelfernandes.org>
>
> rtnl_register_internal() and rtnl_unregister_all tries to directly
> dereference an RCU protected pointed outside RCU read side section.
> While this is Ok to do since a lock is held, let us use the correct
> API to avoid programmer bugs in the future.
>
> This also fixes sparse warnings arising from not using RCU API.
>
> net/core/rtnetlink.c:332:13: warning: incorrect type in assignment
> (different address spaces) net/core/rtnetlink.c:332:13: expected
> struct rtnl_link **tab net/core/rtnetlink.c:332:13: got struct
> rtnl_link *[noderef] <asn:4>*<noident>
>
> Signed-off-by: Joel Fernandes <joel@joelfernandes.org>

First, thank you for doing this!

I was going to complain that these were update-side accesses, but it
looks like rtnl_dereference() already handles both readers and updaters.

So looks good to me, but the maintainers of course have the final word.

Thanx, Paul

> ---
> net/core/rtnetlink.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 5ea1bed08ede..98be4b4818a9 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -188,7 +188,7 @@ static int rtnl_register_internal(struct module *owner,
> msgindex = rtm_msgindex(msgtype);
>
> rtnl_lock();
> - tab = rtnl_msg_handlers[protocol];
> + tab = rtnl_dereference(rtnl_msg_handlers[protocol]);
> if (tab == NULL) {
> tab = kcalloc(RTM_NR_MSGTYPES, sizeof(void *), GFP_KERNEL);
> if (!tab)
> @@ -329,7 +329,7 @@ void rtnl_unregister_all(int protocol)
> BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
>
> rtnl_lock();
> - tab = rtnl_msg_handlers[protocol];
> + tab = rtnl_dereference(rtnl_msg_handlers[protocol]);
> if (!tab) {
> rtnl_unlock();
> return;
> --
> 2.21.0.rc0.258.g878e2cd30e-goog
>

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