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. Any better idea?
