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rtnetlink: get reference on module before invoking handlers
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Add yet another rtnl_register function.  It will be used by modules
that can be removed.

The passed module struct is used to prevent module unload while
a netlink dump is in progress or when a DOIT_UNLOCKED doit callback
is called.

Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Florian Westphal authored and David S. Miller committed Dec 4, 2017
1 parent addf9b9 commit e420251
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Showing 2 changed files with 80 additions and 35 deletions.
2 changes: 2 additions & 0 deletions include/net/rtnetlink.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,8 @@ int __rtnl_register(int protocol, int msgtype,
rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
void rtnl_register(int protocol, int msgtype,
rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
int rtnl_register_module(struct module *owner, int protocol, int msgtype,
rtnl_doit_func, rtnl_dumpit_func, unsigned int flags);
int rtnl_unregister(int protocol, int msgtype);
void rtnl_unregister_all(int protocol);

Expand Down
113 changes: 78 additions & 35 deletions net/core/rtnetlink.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -62,6 +62,7 @@
struct rtnl_link {
rtnl_doit_func doit;
rtnl_dumpit_func dumpit;
struct module *owner;
unsigned int flags;
struct rcu_head rcu;
};
Expand Down Expand Up @@ -129,7 +130,6 @@ EXPORT_SYMBOL(lockdep_rtnl_is_held);
#endif /* #ifdef CONFIG_PROVE_LOCKING */

static struct rtnl_link __rcu **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)
{
Expand Down Expand Up @@ -159,27 +159,10 @@ static struct rtnl_link *rtnl_get_link(int protocol, int msgtype)
return tab[msgtype];
}

/**
* __rtnl_register - Register a rtnetlink message type
* @protocol: Protocol family or PF_UNSPEC
* @msgtype: rtnetlink message type
* @doit: Function pointer called for each request message
* @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
* @flags: rtnl_link_flags to modifiy behaviour of doit/dumpit functions
*
* Registers the specified function pointers (at least one of them has
* to be non-NULL) to be called whenever a request message for the
* specified protocol family and message type is received.
*
* The special protocol family PF_UNSPEC may be used to define fallback
* function pointers for the case when no entry for the specific protocol
* family exists.
*
* Returns 0 on success or a negative error code.
*/
int __rtnl_register(int protocol, int msgtype,
rtnl_doit_func doit, rtnl_dumpit_func dumpit,
unsigned int flags)
static int rtnl_register_internal(struct module *owner,
int protocol, int msgtype,
rtnl_doit_func doit, rtnl_dumpit_func dumpit,
unsigned int flags)
{
struct rtnl_link **tab, *link, *old;
int msgindex;
Expand Down Expand Up @@ -210,6 +193,9 @@ int __rtnl_register(int protocol, int msgtype,
goto unlock;
}

WARN_ON(link->owner && link->owner != owner);
link->owner = owner;

WARN_ON(doit && link->doit && link->doit != doit);
if (doit)
link->doit = doit;
Expand All @@ -228,6 +214,54 @@ int __rtnl_register(int protocol, int msgtype,
rtnl_unlock();
return ret;
}

/**
* rtnl_register_module - Register a rtnetlink message type
*
* @owner: module registering the hook (THIS_MODULE)
* @protocol: Protocol family or PF_UNSPEC
* @msgtype: rtnetlink message type
* @doit: Function pointer called for each request message
* @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
* @flags: rtnl_link_flags to modifiy behaviour of doit/dumpit functions
*
* Like rtnl_register, but for use by removable modules.
*/
int rtnl_register_module(struct module *owner,
int protocol, int msgtype,
rtnl_doit_func doit, rtnl_dumpit_func dumpit,
unsigned int flags)
{
return rtnl_register_internal(owner, protocol, msgtype,
doit, dumpit, flags);
}
EXPORT_SYMBOL_GPL(rtnl_register_module);

/**
* __rtnl_register - Register a rtnetlink message type
* @protocol: Protocol family or PF_UNSPEC
* @msgtype: rtnetlink message type
* @doit: Function pointer called for each request message
* @dumpit: Function pointer called for each dump request (NLM_F_DUMP) message
* @flags: rtnl_link_flags to modifiy behaviour of doit/dumpit functions
*
* Registers the specified function pointers (at least one of them has
* to be non-NULL) to be called whenever a request message for the
* specified protocol family and message type is received.
*
* The special protocol family PF_UNSPEC may be used to define fallback
* function pointers for the case when no entry for the specific protocol
* family exists.
*
* Returns 0 on success or a negative error code.
*/
int __rtnl_register(int protocol, int msgtype,
rtnl_doit_func doit, rtnl_dumpit_func dumpit,
unsigned int flags)
{
return rtnl_register_internal(NULL, protocol, msgtype,
doit, dumpit, flags);
}
EXPORT_SYMBOL_GPL(__rtnl_register);

/**
Expand Down Expand Up @@ -311,8 +345,6 @@ void rtnl_unregister_all(int protocol)

synchronize_net();

while (refcount_read(&rtnl_msg_handlers_ref[protocol]) > 1)
schedule();
kfree(tab);
}
EXPORT_SYMBOL_GPL(rtnl_unregister_all);
Expand Down Expand Up @@ -4372,6 +4404,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
{
struct net *net = sock_net(skb->sk);
struct rtnl_link *link;
struct module *owner;
int err = -EOPNOTSUPP;
rtnl_doit_func doit;
unsigned int flags;
Expand Down Expand Up @@ -4408,24 +4441,32 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
if (!link || !link->dumpit)
goto err_unlock;
}
owner = link->owner;
dumpit = link->dumpit;

refcount_inc(&rtnl_msg_handlers_ref[family]);

if (type == RTM_GETLINK - RTM_BASE)
min_dump_alloc = rtnl_calcit(skb, nlh);

err = 0;
/* need to do this before rcu_read_unlock() */
if (!try_module_get(owner))
err = -EPROTONOSUPPORT;

rcu_read_unlock();

rtnl = net->rtnl;
{
if (err == 0) {
struct netlink_dump_control c = {
.dump = dumpit,
.min_dump_alloc = min_dump_alloc,
.module = owner,
};
err = netlink_dump_start(rtnl, skb, nlh, &c);
/* netlink_dump_start() will keep a reference on
* module if dump is still in progress.
*/
module_put(owner);
}
refcount_dec(&rtnl_msg_handlers_ref[family]);
return err;
}

Expand All @@ -4437,14 +4478,19 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
goto out_unlock;
}

owner = link->owner;
if (!try_module_get(owner)) {
err = -EPROTONOSUPPORT;
goto out_unlock;
}

flags = link->flags;
if (flags & RTNL_FLAG_DOIT_UNLOCKED) {
refcount_inc(&rtnl_msg_handlers_ref[family]);
doit = link->doit;
rcu_read_unlock();
if (doit)
err = doit(skb, nlh, extack);
refcount_dec(&rtnl_msg_handlers_ref[family]);
module_put(owner);
return err;
}
rcu_read_unlock();
Expand All @@ -4455,6 +4501,8 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
err = link->doit(skb, nlh, extack);
rtnl_unlock();

module_put(owner);

return err;

out_unlock:
Expand Down Expand Up @@ -4546,11 +4594,6 @@ static struct pernet_operations rtnetlink_net_ops = {

void __init rtnetlink_init(void)
{
int i;

for (i = 0; i < ARRAY_SIZE(rtnl_msg_handlers_ref); i++)
refcount_set(&rtnl_msg_handlers_ref[i], 1);

if (register_pernet_subsys(&rtnetlink_net_ops))
panic("rtnetlink_init: cannot initialize rtnetlink\n");

Expand Down

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