Commit 187e5b3a authored Aug 15, 2017 by Eric Dumazet Committed by David S. Miller Aug 15, 2017

ipv4: fix NULL dereference in free_fib_info_rcu()



If fi->fib_metrics could not be allocated in fib_create_info()
we attempt to dereference a NULL pointer in free_fib_info_rcu() :

    m = fi->fib_metrics;
    if (m != &dst_default_metrics && atomic_dec_and_test(&m->refcnt))
            kfree(m);

Before my recent patch, we used to call kfree(NULL) and nothing wrong
happened.

Instead of using RCU to defer freeing while we are under memory stress,
it seems better to take immediate action.

This was reported by syzkaller team.

Fixes: 3fb07daf ("ipv4: add reference counting to metrics")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent b3dc8f77

net/ipv4/fib_semantics.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -1083,15 +1083,17 @@ struct fib_info fib_create_info(struct fib_config cfg,
		fi = kzalloc(sizeof(fi)+nhssizeof(struct fib_nh), GFP_KERNEL);
		if (!fi)
		goto failure;
		fib_info_cnt++;
		if (cfg->fc_mx) {
		fi->fib_metrics = kzalloc(sizeof(*fi->fib_metrics), GFP_KERNEL);
		if (!fi->fib_metrics)
		goto failure;
		if (unlikely(!fi->fib_metrics)) {
		kfree(fi);
		return ERR_PTR(err);
		}
		atomic_set(&fi->fib_metrics->refcnt, 1);
		} else
		} else {
		fi->fib_metrics = (struct dst_metrics *)&dst_default_metrics;

		}
		fib_info_cnt++;
		fi->fib_net = net;
		fi->fib_protocol = cfg->fc_protocol;
		fi->fib_scope = cfg->fc_scope;

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