linux-kernel - [PATCH 5.9 32/49] net: tipc: prevent possible null deref of link

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Date:   Sat, 19 Dec 2020 13:58:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Cengiz Can <cengiz@...nel.wtf>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.9 32/49] net: tipc: prevent possible null deref of link

From: Cengiz Can <cengiz@...nel.wtf>

[ Upstream commit 0398ba9e5a4b5675aa571e0445689d3c2e499c2d ]

`tipc_node_apply_property` does a null check on a `tipc_link_entry`
pointer but also accesses the same pointer out of the null check block.

This triggers a warning on Coverity Static Analyzer because we're
implying that `e->link` can BE null.

Move "Update MTU for node link entry" line into if block to make sure
that we're not in a state that `e->link` is null.

Signed-off-by: Cengiz Can <cengiz@...nel.wtf>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/tipc/node.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -2170,9 +2170,11 @@ void tipc_node_apply_property(struct net
 							&xmitq);
 			else if (prop == TIPC_NLA_PROP_MTU)
 				tipc_link_set_mtu(e->link, b->mtu);
+
+			/* Update MTU for node link entry */
+			e->mtu = tipc_link_mss(e->link);
 		}
-		/* Update MTU for node link entry */
-		e->mtu = tipc_link_mss(e->link);
+
 		tipc_node_write_unlock(n);
 		tipc_bearer_xmit(net, bearer_id, &xmitq, &e->maddr, NULL);
 	}