| Message ID | 20230126013521.21836-1-fw@strlen.de |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | [nf] Revert "netfilter: conntrack: fix bug in for_each_sctp_chunk" | expand |
> -----Original Message----- > From: Florian Westphal <fw@strlen.de> > Sent: Thursday, 26 January 2023 02:35 > To: netfilter-devel@vger.kernel.org > Cc: Florian Westphal <fw@strlen.de> > Subject: [PATCH nf] Revert "netfilter: conntrack: fix bug in > for_each_sctp_chunk" > > There is no bug. If sch->length == 0, this would result in an infinite loop, but > first caller, do_basic_checks(), errors out in this case. > Ah yes, perhaps your comment was for [1], where for_each_sctp_chunk() is used only once in nf_conntrack_sctp_packet(), and I didn't check for (sch)->length. The (sch)->length check in do_basic_checks() was almost invisible to me :( [1] https://patchwork.ozlabs.org/project/netfilter-devel/patch/20230111094640.24663-1-sriram.yagnaraman@est.tech/ > After this change, packets with bogus zero-length chunks are no longer > detected as invalid, so revert & add comment wrt. 0 length check. > > Fixes: 98ee00774525 ("netfilter: conntrack: fix bug in for_each_sctp_chunk") > Signed-off-by: Florian Westphal <fw@strlen.de> > --- > It might be a good idea to merge do_basic_checks and sctp_error to avoid > future patches adding for_each_sctp_chunk() earlier in the pipeline. > > net/netfilter/nf_conntrack_proto_sctp.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/net/netfilter/nf_conntrack_proto_sctp.c > b/net/netfilter/nf_conntrack_proto_sctp.c > index 945dd40e7077..2f4459478750 100644 > --- a/net/netfilter/nf_conntrack_proto_sctp.c > +++ b/net/netfilter/nf_conntrack_proto_sctp.c > @@ -142,10 +142,11 @@ static void sctp_print_conntrack(struct seq_file *s, > struct nf_conn *ct) } #endif > > +/* do_basic_checks ensures sch->length > 0, do not use before */ > #define for_each_sctp_chunk(skb, sch, _sch, offset, dataoff, count) \ > for ((offset) = (dataoff) + sizeof(struct sctphdr), (count) = 0; \ > - ((sch) = skb_header_pointer((skb), (offset), sizeof(_sch), &(_sch))) && > \ > - (sch)->length; \ > + (offset) < (skb)->len && \ > + ((sch) = skb_header_pointer((skb), (offset), sizeof(_sch), &(_sch))); > \ > (offset) += (ntohs((sch)->length) + 3) & ~3, (count)++) > > /* Some validity checks to make sure the chunks are fine */ > -- > 2.39.1
diff --git a/net/netfilter/nf_conntrack_proto_sctp.c b/net/netfilter/nf_conntrack_proto_sctp.c index 945dd40e7077..2f4459478750 100644 --- a/net/netfilter/nf_conntrack_proto_sctp.c +++ b/net/netfilter/nf_conntrack_proto_sctp.c @@ -142,10 +142,11 @@ static void sctp_print_conntrack(struct seq_file *s, struct nf_conn *ct) } #endif +/* do_basic_checks ensures sch->length > 0, do not use before */ #define for_each_sctp_chunk(skb, sch, _sch, offset, dataoff, count) \ for ((offset) = (dataoff) + sizeof(struct sctphdr), (count) = 0; \ - ((sch) = skb_header_pointer((skb), (offset), sizeof(_sch), &(_sch))) && \ - (sch)->length; \ + (offset) < (skb)->len && \ + ((sch) = skb_header_pointer((skb), (offset), sizeof(_sch), &(_sch))); \ (offset) += (ntohs((sch)->length) + 3) & ~3, (count)++) /* Some validity checks to make sure the chunks are fine */
There is no bug. If sch->length == 0, this would result in an infinite loop, but first caller, do_basic_checks(), errors out in this case. After this change, packets with bogus zero-length chunks are no longer detected as invalid, so revert & add comment wrt. 0 length check. Fixes: 98ee00774525 ("netfilter: conntrack: fix bug in for_each_sctp_chunk") Signed-off-by: Florian Westphal <fw@strlen.de> --- It might be a good idea to merge do_basic_checks and sctp_error to avoid future patches adding for_each_sctp_chunk() earlier in the pipeline. net/netfilter/nf_conntrack_proto_sctp.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)