On Sun, May 07, 2023 at 01:22:54PM +0200, Florian Westphal wrote: > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > > On Fri, May 05, 2023 at 04:51:13PM +0200, Florian Westphal wrote: > > > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > > > > On Fri, May 05, 2023 at 01:16:53PM +0200, Florian Westphal wrote: > > > > > Keep a per-rule bitmask that tracks registers that have seen a store, > > > > > then reject loads when the accessed registers haven't been flagged. > > > > > > > > > > This changes uabi contract, because we previously allowed this. > > > > > Neither nftables nor iptables-nft create such rules. > > > > > > > > > > In case there is breakage, we could insert an 'store 0 to x' > > > > > immediate expression into the ruleset automatically, but this > > > > > isn't done here. > > > > > > > > > > Let me know if you think the "refuse" approach is too risky. > > > > > > > > Might the NFT_BREAK case defeat this approach? Sequence is: > > > > > > > > 1) expression that writes on register hits NFT_BREAK (nothing is written) > > > > 2) expression that read from register, it reads uninitialized data. > > > > > > > > From ruleset load step, we cannot know if the write fails, because it > > > > is subject to NFT_BREAK. > > > > > > Yes, but its irrelevant: If 1) issues NFT_BREAK, 2) won't execute. > > > > And register tracking is done per rule, given context is per rule too, > > good. > > > > I wonder if it is worth to move the bitmask away from nft_ctx, given > > this structure is stored in the struct nft_trans, hence increasing the > > size of this object which is not required at a later state, maybe > > there is a need for a new container structure that store data useful > > for the initial preparation step of the commit protocol. > > Hmm, this will get messy. > > I only see two alternatives: > > - place the bitmask in the pernet structure. > - add struct nft_expr_ctx as a container structure, which has > nft_ctx as first member and the bitmask as second member, to > be used for NEWRULE and NEWSETELEM instead of nft_ctx. Can the 'level' field be moved to this nft_expr_ctx structure? This field is only used from the preparation phase (not in the commit phase). Probably we need to rename nft_ctx to nft_trans_ctx, so it contains the fields that are needed from the commit phase. Then, re-add a nft_ctx again which contains nft_trans_ctx at the beginning, then the register bitmap and the level field. Thus, any future fields only required by preparation phase only will go in nft_ctx, and fields that are specifically are set up from preparation phase and consumed from commit step go in nft_trans_ctx. It is a bit of churn, but it is probably good to tidy up this for future extensions? Let me know, thanks.
