In the Linux kernel, the following vulnerability has been resolved:
netrom: fix double-free in nr_route_frame()
In nr_route_frame(), old_skb is immediately freed without checking if
nr_neigh->ax25 pointer is NULL. Therefore, if nr_neigh->ax25 is NULL,
the caller function will free old_skb again, causing a double-free bug.
Therefore, to prevent this, we need to modify it to check whether
nr_neigh->ax25 is NULL before freeing old_skb.
References 4
https://git.kernel.org/stable/c/94d1a8bd08af1f4cc345c5c29f5db1ea72b8bb8c
416baaa9-dc9f-4396-8d5f-8c081fb06d67
https://git.kernel.org/stable/c/9f5fa78d9980fe75a69835521627ab7943cb3d67
416baaa9-dc9f-4396-8d5f-8c081fb06d67
https://git.kernel.org/stable/c/ba1096c315283ee3292765f6aea4cca15816c4f7
416baaa9-dc9f-4396-8d5f-8c081fb06d67
https://git.kernel.org/stable/c/bd8955337e3764f912f49b360e176d8aaecf7016
416baaa9-dc9f-4396-8d5f-8c081fb06d67