92234c8f15
While it is currently possible for userspace to specify that an existing XDP program should not be replaced when attaching to an interface, there is no mechanism to safely replace a specific XDP program with another. This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be set along with IFLA_XDP_FD. If set, the kernel will check that the program currently loaded on the interface matches the expected one, and fail the operation if it does not. This corresponds to a 'cmpxchg' memory operation. Setting the new attribute with a negative value means that no program is expected to be attached, which corresponds to setting the UPDATE_IF_NOEXIST flag. A new companion flag, XDP_FLAGS_REPLACE, is also added to explicitly request checking of the EXPECTED_FD attribute. This is needed for userspace to discover whether the kernel supports the new attribute. Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/bpf/158515700640.92963.3551295145441017022.stgit@toke.dk