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. > > 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.
