Patch "mptcp: fix msk traversal in mptcp_nl_cmd_set_flags()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    mptcp: fix msk traversal in mptcp_nl_cmd_set_flags()

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mptcp-fix-msk-traversal-in-mptcp_nl_cmd_set_flags.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9c445865282ef2627077e4847dd29b5a59c4bd9f
Author: Paolo Abeni <pabeni@xxxxxxxxxx>
Date:   Thu Jan 20 16:35:27 2022 -0800

    mptcp: fix msk traversal in mptcp_nl_cmd_set_flags()
    
    [ Upstream commit 8e9eacad7ec7a9cbf262649ebf1fa6e6f6cc7d82 ]
    
    The MPTCP endpoint list is under RCU protection, guarded by the
    pernet spinlock. mptcp_nl_cmd_set_flags() traverses the list
    without acquiring the spin-lock nor under the RCU critical section.
    
    This change addresses the issue performing the lookup and the endpoint
    update under the pernet spinlock.
    
    Fixes: 0f9f696a502e ("mptcp: add set_flags command in PM netlink")
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index bba166ddacc78..7f11eb3e35137 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -469,6 +469,20 @@ __lookup_addr_by_id(struct pm_nl_pernet *pernet, unsigned int id)
 	return NULL;
 }
 
+static struct mptcp_pm_addr_entry *
+__lookup_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *info,
+	      bool lookup_by_id)
+{
+	struct mptcp_pm_addr_entry *entry;
+
+	list_for_each_entry(entry, &pernet->local_addr_list, list) {
+		if ((!lookup_by_id && addresses_equal(&entry->addr, info, true)) ||
+		    (lookup_by_id && entry->addr.id == info->id))
+			return entry;
+	}
+	return NULL;
+}
+
 static int
 lookup_id_by_addr(struct pm_nl_pernet *pernet, const struct mptcp_addr_info *addr)
 {
@@ -1753,18 +1767,21 @@ static int mptcp_nl_cmd_set_flags(struct sk_buff *skb, struct genl_info *info)
 			return -EOPNOTSUPP;
 	}
 
-	list_for_each_entry(entry, &pernet->local_addr_list, list) {
-		if ((!lookup_by_id && addresses_equal(&entry->addr, &addr.addr, true)) ||
-		    (lookup_by_id && entry->addr.id == addr.addr.id)) {
-			mptcp_nl_addr_backup(net, &entry->addr, bkup);
-
-			if (bkup)
-				entry->flags |= MPTCP_PM_ADDR_FLAG_BACKUP;
-			else
-				entry->flags &= ~MPTCP_PM_ADDR_FLAG_BACKUP;
-		}
+	spin_lock_bh(&pernet->lock);
+	entry = __lookup_addr(pernet, &addr.addr, lookup_by_id);
+	if (!entry) {
+		spin_unlock_bh(&pernet->lock);
+		return -EINVAL;
 	}
 
+	if (bkup)
+		entry->flags |= MPTCP_PM_ADDR_FLAG_BACKUP;
+	else
+		entry->flags &= ~MPTCP_PM_ADDR_FLAG_BACKUP;
+	addr = *entry;
+	spin_unlock_bh(&pernet->lock);
+
+	mptcp_nl_addr_backup(net, &addr.addr, bkup);
 	return 0;
 }