bridge: mrp: Fix out-of-bounds read in br_mrp_parse

The issue was reported by syzbot. When the function br_mrp_parse was
called with a valid net_bridge_port, the net_bridge was an invalid
pointer. Therefore the check br->stp_enabled could pass/fail
depending where it was pointing in memory.
The fix consists of setting the net_bridge pointer if the port is a
valid pointer.

Reported-by: syzbot+9c6f0f1f8e32223df9a4@syzkaller.appspotmail.com
Fixes: c81211ee2e45 ("bridge: mrp: Integrate MRP into the bridge")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/bridge/br_mrp_netlink.c b/net/bridge/br_mrp_netlink.c
index 397e7f710772ad57e3377d956ca75d005093d19e..4a08a99519b04f13c7a7c26dc6bbd47ba329ed15 100644 (file)
--- a/net/bridge/br_mrp_netlink.c
+++ b/net/bridge/br_mrp_netlink.c
@@ -27,6 +27,12 @@ int br_mrp_parse(struct net_bridge *br, struct net_bridge_port *p,
        struct nlattr *tb[IFLA_BRIDGE_MRP_MAX + 1];
        int err;
 
+       /* When this function is called for a port then the br pointer is
+        * invalid, therefor set the br to point correctly
+        */
+       if (p)
+               br = p->br;
+
        if (br->stp_enabled != BR_NO_STP) {
                NL_SET_ERR_MSG_MOD(extack, "MRP can't be enabled if STP is already enabled");
                return -EINVAL;