[PATCH] bridge: mrp: Fix out-of-bounds read in br_mrp_parse

[Horatiu Vultur]

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+9c6f0f1f8e32223df...@syzkaller.appspotmail.com
Fixes: 6536993371fa ("bridge: mrp: Integrate MRP into the bridge")
Signed-off-by: Horatiu Vultur <horatiu.vul...@microchip.com>
---
 net/bridge/br_mrp_netlink.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/bridge/br_mrp_netlink.c b/net/bridge/br_mrp_netlink.c
index 397e7f710772a..4a08a99519b04 100644
--- 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;
-- 
2.26.2