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rxrpc: Fix race between conn bundle lookup and bundle removal [ZDI-CAN-15975]

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After rxrpc_unbundle_conn() has removed a connection from a bundle, it
checks to see if there are any conns with available channels and, if not,
removes and attempts to destroy the bundle.

Whilst it does check after grabbing client_bundles_lock that there are no
connections attached, this races with rxrpc_look_up_bundle() retrieving the
bundle, but not attaching a connection for the connection to be attached
later.

There is therefore a window in which the bundle can get destroyed before we
manage to attach a new connection to it.

Fix this by adding an "active" counter to struct rxrpc_bundle:

 (1) rxrpc_connect_call() obtains an active count by prepping/looking up a
     bundle and ditches it before returning.

 (2) If, during rxrpc_connect_call(), a connection is added to the bundle,
     this obtains an active count, which is held until the connection is
     discarded.

 (3) rxrpc_deactivate_bundle() is created to drop an active count on a
     bundle and destroy it when the active count reaches 0.  The active
     count is checked inside client_bundles_lock() to prevent a race with
     rxrpc_look_up_bundle().

 (4) rxrpc_unbundle_conn() then calls rxrpc_deactivate_bundle().

Fixes: 245500d853e9 ("rxrpc: Rewrite the client connection manager")
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-15975
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: zdi-disclosures@trendmicro.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Howells 2022-11-16 14:02:28 +00:00 committed by David S. Miller
parent 302e57f809
commit 3bcd6c7eaa
2 changed files with 24 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
net/rxrpc/ar-internal.h
View File

@ -399,6 +399,7 @@ enum rxrpc_conn_proto_state {
struct rxrpc_bundle {
struct rxrpc_conn_parameters params;
refcount_t ref;
atomic_t active; /* Number of active users */
unsigned int debug_id;
bool try_upgrade; /* True if the bundle is attempting upgrade */
bool alloc_conn; /* True if someone's getting a conn */

38
net/rxrpc/conn_client.c
View File

@ -40,6 +40,8 @@ __read_mostly unsigned long rxrpc_conn_idle_client_fast_expiry = 2 * HZ;
DEFINE_IDR(rxrpc_client_conn_ids);
static DEFINE_SPINLOCK(rxrpc_conn_id_lock);
static void rxrpc_deactivate_bundle(struct rxrpc_bundle *bundle);
/*
* Get a connection ID and epoch for a client connection from the global pool.
* The connection struct pointer is then recorded in the idr radix tree. The
@ -123,6 +125,7 @@ static struct rxrpc_bundle *rxrpc_alloc_bundle(struct rxrpc_conn_parameters *cp,
bundle->params = *cp;
rxrpc_get_peer(bundle->params.peer);
refcount_set(&bundle->ref, 1);
atomic_set(&bundle->active, 1);
spin_lock_init(&bundle->channel_lock);
INIT_LIST_HEAD(&bundle->waiting_calls);
}
@ -149,7 +152,7 @@ void rxrpc_put_bundle(struct rxrpc_bundle *bundle)
dead = __refcount_dec_and_test(&bundle->ref, &r);
_debug("PUT B=%x %d", d, r);
_debug("PUT B=%x %d", d, r - 1);
if (dead)
rxrpc_free_bundle(bundle);
}
@ -338,6 +341,7 @@ found_bundle_free:
rxrpc_free_bundle(candidate);
found_bundle:
rxrpc_get_bundle(bundle);
atomic_inc(&bundle->active);
spin_unlock(&local->client_bundles_lock);
_leave(" = %u [found]", bundle->debug_id);
return bundle;
@ -435,6 +439,7 @@ static void rxrpc_add_conn_to_bundle(struct rxrpc_bundle *bundle, gfp_t gfp)
if (old)
trace_rxrpc_client(old, -1, rxrpc_client_replace);
candidate->bundle_shift = shift;
atomic_inc(&bundle->active);
bundle->conns[i] = candidate;
for (j = 0; j < RXRPC_MAXCALLS; j++)
set_bit(shift + j, &bundle->avail_chans);
@ -725,6 +730,7 @@ granted_channel:
smp_rmb();
out_put_bundle:
rxrpc_deactivate_bundle(bundle);
rxrpc_put_bundle(bundle);
out:
_leave(" = %d", ret);
@ -900,9 +906,8 @@ out:
static void rxrpc_unbundle_conn(struct rxrpc_connection *conn)
{
struct rxrpc_bundle *bundle = conn->bundle;
struct rxrpc_local *local = bundle->params.local;
unsigned int bindex;
bool need_drop = false, need_put = false;
bool need_drop = false;
int i;
_enter("C=%x", conn->debug_id);
@ -921,15 +926,22 @@ static void rxrpc_unbundle_conn(struct rxrpc_connection *conn)
}
spin_unlock(&bundle->channel_lock);
/* If there are no more connections, remove the bundle */
if (!bundle->avail_chans) {
_debug("maybe unbundle");
spin_lock(&local->client_bundles_lock);
if (need_drop) {
rxrpc_deactivate_bundle(bundle);
rxrpc_put_connection(conn);
}
}
for (i = 0; i < ARRAY_SIZE(bundle->conns); i++)
if (bundle->conns[i])
break;
if (i == ARRAY_SIZE(bundle->conns) && !bundle->params.exclusive) {
/*
* Drop the active count on a bundle.
*/
static void rxrpc_deactivate_bundle(struct rxrpc_bundle *bundle)
{
struct rxrpc_local *local = bundle->params.local;
bool need_put = false;
if (atomic_dec_and_lock(&bundle->active, &local->client_bundles_lock)) {
if (!bundle->params.exclusive) {
_debug("erase bundle");
rb_erase(&bundle->local_node, &local->client_bundles);
need_put = true;
@ -939,10 +951,6 @@ static void rxrpc_unbundle_conn(struct rxrpc_connection *conn)
if (need_put)
rxrpc_put_bundle(bundle);
}
if (need_drop)
rxrpc_put_connection(conn);
_leave("");
}
/*