On Mon, Jul 13, 2020 at 10:47 AM Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> wrote: > > Run a BPF program before looking up a listening socket on the receive path. > Program selects a listening socket to yield as result of socket lookup by > calling bpf_sk_assign() helper and returning SK_PASS code. Program can > revert its decision by assigning a NULL socket with bpf_sk_assign(). > > Alternatively, BPF program can also fail the lookup by returning with > SK_DROP, or let the lookup continue as usual with SK_PASS on return, when > no socket has not been selected with bpf_sk_assign(). Other return values you probably meant "no socket has been selected"? > are treated the same as SK_DROP. Why not enforce it instead? Check check_return_code() in verifier.c, it's trivial to do it for SK_LOOKUP. > > This lets the user match packets with listening sockets freely at the last > possible point on the receive path, where we know that packets are destined > for local delivery after undergoing policing, filtering, and routing. > > With BPF code selecting the socket, directing packets destined to an IP > range or to a port range to a single socket becomes possible. > > In case multiple programs are attached, they are run in series in the order > in which they were attached. The end result is determined from return codes > of all the programs according to following rules: > > 1. If any program returned SK_PASS and selected a valid socket, the socket > is used as result of socket lookup. > 2. If more than one program returned SK_PASS and selected a socket, > last selection takes effect. > 3. If any program returned SK_DROP or an invalid return code, and no > program returned SK_PASS and selected a socket, socket lookup fails > with -ECONNREFUSED. > 4. If all programs returned SK_PASS and none of them selected a socket, > socket lookup continues to htable-based lookup. > > Suggested-by: Marek Majkowski <marek@xxxxxxxxxxxxxx> > Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> > --- > > Notes: > v4: > - Reduce BPF sk_lookup prog return codes to SK_PASS/SK_DROP. (Lorenz) your description above still assumes prog can return something besides SK_PASS and SK_DROP? > - Default to drop & warn on illegal return value from BPF prog. (Lorenz) > - Rename netns_bpf_attach_type_enable/disable to _need/unneed. (Lorenz) > - Export bpf_sk_lookup_enabled symbol for CONFIG_IPV6=m (kernel test robot) > - Invert return value from bpf_sk_lookup_run_v4 to true on skip reuseport. > - Move dedicated prog_array runner close to its callers in filter.h. > > v3: > - Use a static_key to minimize the hook overhead when not used. (Alexei) > - Adapt for running an array of attached programs. (Alexei) > - Adapt for optionally skipping reuseport selection. (Martin) > > include/linux/filter.h | 102 +++++++++++++++++++++++++++++++++++++ > kernel/bpf/net_namespace.c | 32 +++++++++++- > net/core/filter.c | 3 ++ > net/ipv4/inet_hashtables.c | 31 +++++++++++ > 4 files changed, 167 insertions(+), 1 deletion(-) > > diff --git a/include/linux/filter.h b/include/linux/filter.h > index 380746f47fa1..b9ad0fdabca5 100644 > --- a/include/linux/filter.h > +++ b/include/linux/filter.h > @@ -1295,4 +1295,106 @@ struct bpf_sk_lookup_kern { > bool no_reuseport; > }; > > +extern struct static_key_false bpf_sk_lookup_enabled; > + > +/* Runners for BPF_SK_LOOKUP programs to invoke on socket lookup. > + * > + * Allowed return values for a BPF SK_LOOKUP program are SK_PASS and > + * SK_DROP. Any other return value is treated as SK_DROP. Their > + * meaning is as follows: > + * > + * SK_PASS && ctx.selected_sk != NULL: use selected_sk as lookup result > + * SK_PASS && ctx.selected_sk == NULL: continue to htable-based socket lookup > + * SK_DROP : terminate lookup with -ECONNREFUSED > + * > + * This macro aggregates return values and selected sockets from > + * multiple BPF programs according to following rules: > + * > + * 1. If any program returned SK_PASS and a non-NULL ctx.selected_sk, > + * macro result is SK_PASS and last ctx.selected_sk is used. > + * 2. If any program returned non-SK_PASS return value, > + * macro result is the last non-SK_PASS return value. > + * 3. Otherwise result is SK_PASS and ctx.selected_sk is NULL. > + * > + * Caller must ensure that the prog array is non-NULL, and that the > + * array as well as the programs it contains remain valid. > + */ > +#define BPF_PROG_SK_LOOKUP_RUN_ARRAY(array, ctx, func) \ > + ({ \ > + struct bpf_sk_lookup_kern *_ctx = &(ctx); \ > + struct bpf_prog_array_item *_item; \ > + struct sock *_selected_sk; \ > + struct bpf_prog *_prog; \ > + u32 _ret, _last_ret; \ > + bool _no_reuseport; \ > + \ > + migrate_disable(); \ > + _last_ret = SK_PASS; \ > + _selected_sk = NULL; \ > + _no_reuseport = false; \ these three could be moved before migrate_disable(), or even better just initialize corresponding variables above? > + _item = &(array)->items[0]; \ > + while ((_prog = READ_ONCE(_item->prog))) { \ > + /* restore most recent selection */ \ > + _ctx->selected_sk = _selected_sk; \ > + _ctx->no_reuseport = _no_reuseport; \ > + \ > + _ret = func(_prog, _ctx); \ > + if (_ret == SK_PASS) { \ > + /* remember last non-NULL socket */ \ > + if (_ctx->selected_sk) { \ > + _selected_sk = _ctx->selected_sk; \ > + _no_reuseport = _ctx->no_reuseport; \ > + } \ > + } else { \ > + /* remember last non-PASS ret code */ \ > + _last_ret = _ret; \ > + } \ > + _item++; \ > + } \ > + _ctx->selected_sk = _selected_sk; \ > + _ctx->no_reuseport = _no_reuseport; \ > + migrate_enable(); \ > + _ctx->selected_sk ? SK_PASS : _last_ret; \ > + }) > + [...]