bearer_disable() frees b->disc with tipc_disc_delete()'s plain kfree(),
but tipc_disc_rcv() still dereferences b->disc in RX softirq under
rcu_read_lock() (tipc_udp_recv -> tipc_rcv -> tipc_disc_rcv).
L2 bearers are safe thanks to the synchronize_net() in
tipc_disable_l2_media(), but the UDP bearer defers that call to the
cleanup_bearer() workqueue, so the discoverer is freed with no grace
period:
BUG: KASAN: slab-use-after-free in tipc_disc_rcv (net/tipc/discover.c:149)
Read of size 8 at addr ffff88802348b728 by task poc_tipc/184
tipc_disc_rcv (net/tipc/discover.c:149)
tipc_rcv (net/tipc/node.c:2126)
tipc_udp_recv (net/tipc/udp_media.c:391)
udp_rcv (net/ipv4/udp.c:2643)
ip_local_deliver_finish (net/ipv4/ip_input.c:241)
Freed by task 181:
kfree (mm/slub.c:6565)
bearer_disable (net/tipc/bearer.c:418)
tipc_nl_bearer_disable (net/tipc/bearer.c:1001)
The bearer is freed with kfree_rcu(); free the discoverer the same way.
Add an rcu_head to struct tipc_discoverer and free it and its skb from an
RCU callback.
Reachable from an unprivileged user namespace: the TIPCv2 genl family is
netnsok and its bearer commands have no GENL_ADMIN_PERM. Needs CONFIG_TIPC
and CONFIG_TIPC_MEDIA_UDP.
Fixes: 25b0b9c4e835 ("tipc: handle collisions of 32-bit node address hash values")
Reported-by: Xiang Mei
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi
---
net/tipc/discover.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/net/tipc/discover.c b/net/tipc/discover.c
index 3e54d2df5683a..34dbe5ad10e09 100644
--- a/net/tipc/discover.c
+++ b/net/tipc/discover.c
@@ -58,6 +58,7 @@
* @skb: request message to be (repeatedly) sent
* @timer: timer governing period between requests
* @timer_intv: current interval between requests (in ms)
+ * @rcu: RCU head for deferred freeing
*/
struct tipc_discoverer {
u32 bearer_id;
@@ -69,6 +70,7 @@ struct tipc_discoverer {
struct sk_buff *skb;
struct timer_list timer;
unsigned long timer_intv;
+ struct rcu_head rcu;
};
/**
@@ -382,6 +384,14 @@ int tipc_disc_create(struct net *net, struct tipc_bearer *b,
return 0;
}
+static void tipc_disc_free_rcu(struct rcu_head *rp)
+{
+ struct tipc_discoverer *d = container_of(rp, struct tipc_discoverer, rcu);
+
+ kfree_skb(d->skb);
+ kfree(d);
+}
+
/**
* tipc_disc_delete - destroy object sending periodic link setup requests
* @d: ptr to link dest structure
@@ -389,8 +399,7 @@ int tipc_disc_create(struct net *net, struct tipc_bearer *b,
void tipc_disc_delete(struct tipc_discoverer *d)
{
timer_shutdown_sync(&d->timer);
- kfree_skb(d->skb);
- kfree(d);
+ call_rcu(&d->rcu, tipc_disc_free_rcu);
}
/**
--
2.43.0