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flow_dissector: Fix potential use-after-free on BPF_PROG_DETACH

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Call to bpf_prog_put(), with help of call_rcu(), queues an RCU-callback to
free the program once a grace period has elapsed. The callback can run
together with new RCU readers that started after the last grace period.
New RCU readers can potentially see the "old" to-be-freed or already-freed
pointer to the program object before the RCU update-side NULLs it.

Reorder the operations so that the RCU update-side resets the protected
pointer before the end of the grace period after which the program will be
freed.

Fixes: d58e468b11 ("flow_dissector: implements flow dissector BPF hook")
Reported-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Petar Penkov <ppenkov@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Jakub Sitnicki 2019-08-21 14:17:20 +02:00 committed by Daniel Borkmann
parent 3035bb72ee
commit db38de3968
1 changed files with 1 additions and 1 deletions
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2
net/core/flow_dissector.c
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@ -142,8 +142,8 @@ int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
mutex_unlock(&flow_dissector_mutex);
return -ENOENT;
}
bpf_prog_put(attached);
RCU_INIT_POINTER(net->flow_dissector_prog, NULL);
bpf_prog_put(attached);
mutex_unlock(&flow_dissector_mutex);
return 0;
}