From 507c2f1d2936e07aef83734983a36df01b458ef9 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 13 Oct 2021 15:21:38 +0200 Subject: net, neigh: Add build-time assertion to avoid neigh->flags overflow 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 2c611ad97a82 ("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 Signed-off-by: Daniel Borkmann Reviewed-by: David Ahern Signed-off-by: Jakub Kicinski --- net/core/neighbour.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'net/core/neighbour.c') diff --git a/net/core/neighbour.c b/net/core/neighbour.c index eae73efa9245..4fc601f9cd06 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -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) { -- cgit