net, neigh: Extend neigh->flags to 32 bit to allow for extensions
Currently, all bits in struct ndmsg's ndm_flags are used up with the most recent addition of 435f2e7c ("net: bridge: add support for sticky fdb entries"). This makes it impossible to extend the neighboring subsystem with new NTF_* flags: struct ndmsg { __u8 ndm_family; __u8 ndm_pad1; __u16 ndm_pad2; __s32 ndm_ifindex; __u16 ndm_state; __u8 ndm_flags; __u8 ndm_type; }; There are ndm_pad{1,2} attributes which are not used. However, due to uncareful design, the kernel does not enforce them to be zero upon new neighbor entry addition, and given they've been around forever, it is not possible to reuse them today due to risk of breakage. One option to overcome this limitation is to add a new NDA_FLAGS_EXT attribute for extended flags. In struct neighbour, there is a 3 byte hole between protocol and ha_lock, which allows neigh->flags to be extended from 8 to 32 bits while still being on the same cacheline as before. This also allows for all future NTF_* flags being in neigh->flags rather than yet another flags field. Unknown flags in NDA_FLAGS_EXT will be rejected by the kernel. Co-developed-by:Daniel Borkmann <daniel@iogearbox.net> Signed-off-by:
Daniel Borkmann <daniel@iogearbox.net> Signed-off-by:
Roopa Prabhu <roopa@nvidia.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
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3dc20f47