From: Geliang Tang <tanggeliang@kylinos.cn>

In mptcp_pm_userspace_get_local_id(), the address entry is looked up under
spinlock, but its id is read after dropping the lock. A concurrent deletion
can free the entry between the unlock and the read, leading to UAF.

Fix by copying the id into a local variable while still holding the lock,
and use -1 as a "not found" sentinel.

Fixes: f012d796a6de ("mptcp: check addrs list in userspace_pm_get_local_id")
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/pm_userspace.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index ad6ba658e5a5..8a5cf5ed8f7b 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -132,12 +132,14 @@ static int mptcp_pm_userspace_get_local_id(struct mptcp_sock *msk,
 	__be16 msk_sport =  ((struct inet_sock *)
 			     inet_sk((struct sock *)msk))->inet_sport;
 	struct mptcp_pm_addr_entry *entry;
+	int id;
 
 	spin_lock_bh(&msk->pm.lock);
 	entry = mptcp_userspace_pm_lookup_addr(msk, &skc->addr);
+	id = entry ? entry->addr.id : -1;
 	spin_unlock_bh(&msk->pm.lock);
-	if (entry)
-		return entry->addr.id;
+	if (id != -1)
+		return id;
 
 	if (skc->addr.port == msk_sport)
 		skc->addr.port = 0;
-- 
2.53.0

Hi Geliang,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal (except selftest_mptcp_join): Unstable: 1 failed test(s): selftest_simult_flows ⚠️ 
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Success! ✅
- KVM Validation: debug (only selftest_mptcp_join): Success! ✅
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/28424886662

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/0fe82a09beee
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1118662


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)