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. Thanks. > > > > > Fixes: e215dab1c490 ("security: call security_sctp_assoc_request in sctp_sf_do_5_1D_ce") > > Reported-by: Yi Chen <yiche@xxxxxxxxxx> > > Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx> > > --- > > net/sctp/sm_statefuns.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c > > index 7f342bc12735..883f9b849ee5 100644 > > --- a/net/sctp/sm_statefuns.c > > +++ b/net/sctp/sm_statefuns.c > > @@ -781,7 +781,7 @@ enum sctp_disposition sctp_sf_do_5_1D_ce(struct net *net, > > } > > } > > > > - if (security_sctp_assoc_request(new_asoc, chunk->skb)) { > > + if (security_sctp_assoc_request(new_asoc, chunk->head_skb ?: chunk->skb)) { > > sctp_association_free(new_asoc); > > return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands); > > } > > @@ -2262,7 +2262,7 @@ enum sctp_disposition sctp_sf_do_5_2_4_dupcook( > > } > > > > /* Update socket peer label if first association. */ > > - if (security_sctp_assoc_request(new_asoc, chunk->skb)) { > > + if (security_sctp_assoc_request(new_asoc, chunk->head_skb ?: chunk->skb)) { > > sctp_association_free(new_asoc); > > return sctp_sf_pdiscard(net, ep, asoc, type, arg, commands); > > } > > -- > > 2.31.1 > > > > -- > Ondrej Mosnacek > Software Engineer, Linux Security - SELinux kernel > Red Hat, Inc. >
