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[ Upstream commit2660a544fd] sk->sk_prot->sock_is_readable is a valid function pointer when sk resides in a sockmap. After the last sk_psock_put() (which usually happens when socket is removed from sockmap), sk->sk_prot gets restored and sk->sk_prot->sock_is_readable becomes NULL. This makes sk_is_readable() racy, if the value of sk->sk_prot is reloaded after the initial check. Which in turn may lead to a null pointer dereference. Ensure the function pointer does not turn NULL after the check. Fixes:8934ce2fd0("bpf: sockmap redirect ingress support") Suggested-by: Jakub Sitnicki <jakub@cloudflare.com> Signed-off-by: Michal Luczaj <mhal@rbox.co> Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/20250609-skisreadable-toctou-v1-1-d0dfb2d62c37@rbox.co Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>