fib_trie: Avoid NULL pointer if local table is not allocated

The function fib_unmerge assumed the local table had already been
allocated.  If that is not the case however when custom rules are applied
then this can result in a NULL pointer dereference.

In order to prevent this we must check the value of the local table pointer
and if it is NULL simply return 0 as there is no local table to separate
from the main.

Fixes: 0ddcf43d5 ("ipv4: FIB Local/MAIN table collapse")
Reported-by: Madhu Challa <challa@noironetworks.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index c1caf9ded280c5161cb1f0cbdd5c2433eb2ba12c..e5b6b0534c5f5e90f9369cafec3c6089d6ebada4 100644 (file)
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -156,9 +156,12 @@ int fib_unmerge(struct net *net)
 {
        struct fib_table *old, *new;
 
+       /* attempt to fetch local table if it has been allocated */
        old = fib_get_table(net, RT_TABLE_LOCAL);
-       new = fib_trie_unmerge(old);
+       if (!old)
+               return 0;
 
+       new = fib_trie_unmerge(old);
        if (!new)
                return -ENOMEM;