Re: [syzbot] [mptcp?] KASAN: slab-use-after-free Read in __timer_delete_sync

From: Edward Adam Davis
Date: Tue Sep 10 2024 - 04:04:14 EST


entry need to be protected by pm.lock.

#syz test

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 3e4ad801786f..b09268fc7fc9 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -329,17 +329,28 @@ struct mptcp_pm_add_entry *
mptcp_pm_del_add_timer(struct mptcp_sock *msk,
const struct mptcp_addr_info *addr, bool check_id)
{
- struct mptcp_pm_add_entry *entry;
struct sock *sk = (struct sock *)msk;
+ struct timer_list *add_timer = NULL;
+ struct mptcp_pm_add_entry *entry;

spin_lock_bh(&msk->pm.lock);
entry = mptcp_lookup_anno_list_by_saddr(msk, addr);
- if (entry && (!check_id || entry->addr.id == addr->id))
+ if (entry && (!check_id || entry->addr.id == addr->id)) {
entry->retrans_times = ADD_ADDR_RETRANS_MAX;
+ add_timer = &entry->add_timer;
+ }
spin_unlock_bh(&msk->pm.lock);

- if (entry && (!check_id || entry->addr.id == addr->id))
- sk_stop_timer_sync(sk, &entry->add_timer);
+ /* no lock, because sk_stop_timer_sync() is calling del_timer_sync() */
+ if (add_timer)
+ sk_stop_timer_sync(sk, add_timer);
+
+ spin_lock_bh(&msk->pm.lock);
+ if (!check_id && entry) {
+ list_del(&entry->list);
+ kfree(entry);
+ }
+ spin_unlock_bh(&msk->pm.lock);

return entry;
}
@@ -1426,16 +1437,7 @@ int mptcp_pm_nl_get_flags_and_ifindex_by_id(struct mptcp_sock *msk, unsigned int
static bool remove_anno_list_by_saddr(struct mptcp_sock *msk,
const struct mptcp_addr_info *addr)
{
- struct mptcp_pm_add_entry *entry;
-
- entry = mptcp_pm_del_add_timer(msk, addr, false);
- if (entry) {
- list_del(&entry->list);
- kfree(entry);
- return true;
- }
-
- return false;
+ return mptcp_pm_del_add_timer(msk, addr, false) != NULL;
}

static bool mptcp_pm_remove_anno_addr(struct mptcp_sock *msk,
--
2.43.0