On Tue, Apr 5, 2022 at 1:58 PM Xin Long <lucien.xin@xxxxxxxxx> wrote: > On Mon, Apr 4, 2022 at 6:15 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote: > > > > Adding LSM and SELinux lists to CC for awareness; the original patch > > is available at: > > https://lore.kernel.org/netdev/a77a584b3ce9761eb5dda5828192e1cab94571f0.1649037151.git.lucien.xin@xxxxxxxxx/T/ > > https://patchwork.kernel.org/project/netdevbpf/patch/a77a584b3ce9761eb5dda5828192e1cab94571f0.1649037151.git.lucien.xin@xxxxxxxxx/ > > > > On Mon, Apr 4, 2022 at 3:53 AM Xin Long <lucien.xin@xxxxxxxxx> wrote: > > > > > > Yi Chen reported an unexpected sctp connection abort, and it occurred when > > > COOKIE_ECHO is bundled with DATA Fragment by SCTP HW GSO. As the IP header > > > is included in chunk->head_skb instead of chunk->skb, it failed to check > > > IP header version in security_sctp_assoc_request(). > > > > > > According to Ondrej, SELinux only looks at IP header (address and IPsec > > > options) and XFRM state data, and these are all included in head_skb for > > > SCTP HW GSO packets. So fix it by using head_skb when calling > > > security_sctp_assoc_request() in processing COOKIE_ECHO. > > > > The logic looks good to me, but I still have one unanswered concern. > > The head_skb member of struct sctp_chunk is defined inside a union: > > > > struct sctp_chunk { > > [...] > > union { > > /* In case of GSO packets, this will store the head one */ > > struct sk_buff *head_skb; > > /* In case of auth enabled, this will point to the shkey */ > > struct sctp_shared_key *shkey; > > }; > > [...] > > }; > > > > What guarantees that this chunk doesn't have "auth enabled" and the > > head_skb pointer isn't actually a non-NULL shkey pointer? Maybe it's > > obvious to a Linux SCTP expert, but at least for me as an outsider it > > isn't - that's usually a good hint that there should be a code comment > > explaining it. > Hi Ondrej, > > shkey is for tx skbs only, while head_skb is for skbs on rx path. That makes sense, thanks. I would still be happier if this was documented, but the comment would best fit in the struct sctp_chunk definition and that wouldn't fit in this patch... Actually I have one more question - what about the security_sctp_assoc_established() call in sctp_sf_do_5_1E_ca()? Is COOKIE ACK guaranteed to be never bundled? -- Ondrej Mosnacek Software Engineer, Linux Security - SELinux kernel Red Hat, Inc.
