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net, neigh: Add build-time assertion to avoid neigh->flags overflow

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Currently, NDA_FLAGS_EXT flags allow a maximum of 24 bits to be used for
extended neighbor flags. These are eventually fed into neigh->flags by
shifting with NTF_EXT_SHIFT as per commit 2c611ad97a ("net, neigh:
Extend neigh->flags to 32 bit to allow for extensions").

If really ever needed in future, the full 32 bits from NDA_FLAGS_EXT can
be used, it would only require to move neigh->flags from u32 to u64 inside
the kernel.

Add a build-time assertion such that when extending the NTF_EXT_MASK with
new bits, we'll trigger an error once we surpass the 24th bit. This assumes
that no bit holes in new NTF_EXT_* flags will slip in from UAPI, but I
think this is reasonable to assume.

Suggested-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Daniel Borkmann 2021-10-13 15:21:38 +02:00 • committed by Jakub Kicinski
parent 20d446f24f
commit 507c2f1d29
1 changed files with 3 additions and 0 deletions
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3
net/core/neighbour.c
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@ -1940,6 +1940,9 @@ static int neigh_add(struct sk_buff *skb, struct nlmsghdr *nlh,
NL_SET_ERR_MSG(extack, "Invalid extended flags");
goto out;
}
BUILD_BUG_ON(sizeof(neigh->flags) * BITS_PER_BYTE <
(sizeof(ndm->ndm_flags) * BITS_PER_BYTE +
hweight32(NTF_EXT_MASK)));
ndm_flags |= (ext << NTF_EXT_SHIFT);
}
if (ndm->ndm_ifindex) {