| From | Greg Kroah-Hartman <> | Subject | [PATCH 5.2 063/124] flow_dissector: Fix potential use-after-free on BPF_PROG_DETACH | Date | Fri, 20 Sep 2019 00:02:31 +0200 |
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From: Jakub Sitnicki <jakub@cloudflare.com>
[ Upstream commit db38de39684dda2bf307f41797db2831deba64e9 ]
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: d58e468b1112 ("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> Signed-off-by: Sasha Levin <sashal@kernel.org> --- net/core/flow_dissector.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index edd622956083d..b15c0c0f6e557 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -138,8 +138,8 @@ 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; } -- 2.20.1
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