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rtnetlink: add reference counting to prevent module unload while dump is in progress

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I don't see what prevents rmmod (unregister_all is called) while a dump
is active.

Even if we'd add rtnl lock/unlock pair to unregister_all (as done here),
thats not enough either as rtnl_lock is released right before the dump
process starts.

So this adds a refcount:
 * acquire rtnl mutex
 * bump refcount
 * release mutex
 * start the dump

... and make unregister_all remove the callbacks (no new dumps possible)
and then wait until refcount is 0.

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2017-08-09 20:41:49 +02:00 committed by David S. Miller
parent b97bac64a5
commit 019a316992
1 changed files with 13 additions and 1 deletions
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14
net/core/rtnetlink.c
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@ -127,6 +127,7 @@ EXPORT_SYMBOL(lockdep_rtnl_is_held);
#endif /* #ifdef CONFIG_PROVE_LOCKING */
static struct rtnl_link *rtnl_msg_handlers[RTNL_FAMILY_MAX + 1];
static refcount_t rtnl_msg_handlers_ref[RTNL_FAMILY_MAX + 1];
static inline int rtm_msgindex(int msgtype)
{
@ -272,10 +273,18 @@ EXPORT_SYMBOL_GPL(rtnl_unregister);
*/
void rtnl_unregister_all(int protocol)
{
struct rtnl_link *handlers;
BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
kfree(rtnl_msg_handlers[protocol]);
rtnl_lock();
handlers = rtnl_msg_handlers[protocol];
rtnl_msg_handlers[protocol] = NULL;
rtnl_unlock();
while (refcount_read(&rtnl_msg_handlers_ref[protocol]) > 0)
schedule();
kfree(handlers);
}
EXPORT_SYMBOL_GPL(rtnl_unregister_all);
@ -4173,6 +4182,8 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
if (dumpit == NULL)
return -EOPNOTSUPP;
refcount_inc(&rtnl_msg_handlers_ref[family]);
if (type == RTM_GETLINK)
min_dump_alloc = rtnl_calcit(skb, nlh);
@ -4186,6 +4197,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
err = netlink_dump_start(rtnl, skb, nlh, &c);
}
rtnl_lock();
refcount_dec(&rtnl_msg_handlers_ref[family]);
return err;
}