On Wed, Nov 30, 2022 at 6:42 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > The bpf_ct_set_nat_info() kfunc is defined in the nf_nat.ko module, and > takes as a parameter the nf_conn___init struct, which is allocated through > the bpf_xdp_ct_alloc() helper defined in the nf_conntrack.ko module. > However, because kernel modules can't deduplicate BTF types between each > other, and the nf_conn___init struct is not referenced anywhere in vmlinux > BTF, this leads to two distinct BTF IDs for the same type (one in each > module). This confuses the verifier, as described here: > Argh, shouldn't have wasted writing [1], but oh well. [1] https://lore.kernel.org/bpf/CAEf4Bza2xDZ45kxxa3dg1C_RWE=UB5UFYEuFp6rbXgX=LRHv-A@xxxxxxxxxxxxxx/ > https://lore.kernel.org/all/87leoh372s.fsf@xxxxxxx/ > > As a workaround, add a dummy pointer to the type in net/filter.c, so the > type definition gets included in vmlinux BTF. This way, both modules can > refer to the same type ID (as they both build on top of vmlinux BTF), and > the verifier is no longer confused. > > Fixes: 820dc0523e05 ("net: netfilter: move bpf_ct_set_nat_info kfunc in nf_nat_bpf.c") > Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx> > --- > net/core/filter.c | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index bb0136e7a8e4..1bdf9efe8593 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -80,6 +80,7 @@ > #include <net/tls.h> > #include <net/xdp.h> > #include <net/mptcp.h> > +#include <net/netfilter/nf_conntrack_bpf.h> > > static const struct bpf_func_proto * > bpf_sk_base_func_proto(enum bpf_func_id func_id); > @@ -11531,3 +11532,17 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id) > > return func; > } > + > +#if IS_MODULE(CONFIG_NF_CONNTRACK) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES) > +/* The nf_conn___init type is used in the NF_CONNTRACK kfuncs. The kfuncs are > + * defined in two different modules, and we want to be able to use them > + * interchangably with the same BTF type ID. Because modules can't de-duplicate > + * BTF IDs between each other, we need the type to be referenced in the vmlinux > + * BTF or the verifier will get confused about the different types. So we add > + * this dummy pointer to serve as a type reference which will be included in > + * vmlinux BTF, allowing both modules to refer to the same type ID. > + * > + * We use a pointer as that is smaller than an instance of the struct. > + */ > +const struct nf_conn___init *ctinit; > +#endif Use BTF_TYPE_EMIT() instead maybe? > -- > 2.38.1 >
