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mctp: locking, lifetime and validity changes for sk_keys

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We will want to invalidate sk_keys in a future change, which will
require a boolean flag to mark invalidated items in the socket & net
namespace lists. We'll also need to take a reference to keys, held over
non-atomic contexts, so we need a refcount on keys also.

This change adds a validity flag (currently always true) and refcount to
struct mctp_sk_key.  With a refcount on the keys, using RCU no longer
makes much sense; we have exact indications on the lifetime of keys. So,
we also change the RCU list traversal to a locked implementation.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jeremy Kerr
2021-09-29 15:26:07 +08:00
committed by David S. Miller
parent 1f6c77ac9e
commit 73c618456d
3 changed files with 125 additions and 53 deletions
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46
include/net/mctp.h
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@@ -67,30 +67,36 @@ struct mctp_sock {
/* Key for matching incoming packets to sockets or reassembly contexts.
* Packets are matched on (src,dest,tag).
*
* Lifetime requirements:
* Lifetime / locking requirements:
*
* - keys are free()ed via RCU
* - individual key data (ie, the struct itself) is protected by key->lock;
* changes must be made with that lock held.
*
* - the lookup fields: peer_addr, local_addr and tag are set before the
* key is added to lookup lists, and never updated.
*
* - A ref to the key must be held (throuh key->refs) if a pointer to the
* key is to be accessed after key->lock is released.
*
* - a mctp_sk_key contains a reference to a struct sock; this is valid
* for the life of the key. On sock destruction (through unhash), the key is
* removed from lists (see below), and will not be observable after a RCU
* grace period.
*
* any RX occurring within that grace period may still queue to the socket,
* but will hit the SOCK_DEAD case before the socket is freed.
* removed from lists (see below), and marked invalid.
*
* - these mctp_sk_keys appear on two lists:
* 1) the struct mctp_sock->keys list
* 2) the struct netns_mctp->keys list
*
* updates to either list are performed under the netns_mctp->keys
* lock.
* presences on these lists requires a (single) refcount to be held; both
* lists are updated as a single operation.
*
* Updates and lookups in either list are performed under the
* netns_mctp->keys lock. Lookup functions will need to lock the key and
* take a reference before unlocking the keys_lock. Consequently, the list's
* keys_lock *cannot* be acquired with the individual key->lock held.
*
* - a key may have a sk_buff attached as part of an in-progress message
* reassembly (->reasm_head). The reassembly context is protected by
* reasm_lock, which may be acquired with the keys lock (above) held, if
* necessary. Consequently, keys lock *cannot* be acquired with the
* reasm_lock held.
* reassembly (->reasm_head). The reasm data is protected by the individual
* key->lock.
*
* - there are two destruction paths for a mctp_sk_key:
*
@@ -116,14 +122,22 @@ struct mctp_sk_key {
/* per-socket list */
struct hlist_node sklist;
/* lock protects against concurrent updates to the reassembly and
* expiry data below.
*/
spinlock_t lock;
/* Keys are referenced during the output path, which may sleep */
refcount_t refs;
/* incoming fragment reassembly context */
spinlock_t reasm_lock;
struct sk_buff *reasm_head;
struct sk_buff **reasm_tailp;
bool reasm_dead;
u8 last_seq;
struct rcu_head rcu;
/* key validity */
bool valid;
};
struct mctp_skb_cb {
@@ -191,6 +205,8 @@ int mctp_do_route(struct mctp_route *rt, struct sk_buff *skb);
int mctp_local_output(struct sock *sk, struct mctp_route *rt,
struct sk_buff *skb, mctp_eid_t daddr, u8 req_tag);
void mctp_key_unref(struct mctp_sk_key *key);
/* routing <--> device interface */
unsigned int mctp_default_net(struct net *net);
int mctp_default_net_set(struct net *net, unsigned int index);