| Message ID | 160109442512.6363.1622656051946413257.stgit@john-Precision-5820-Tower |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | Add skb_adjust_room() for SK_SKB | expand |
On 9/26/20 6:27 AM, John Fastabend wrote: > This implements a new helper skb_adjust_room() so users can push/pop > extra bytes from a BPF_SK_SKB_STREAM_VERDICT program. > > Some protocols may include headers and other information that we may > not want to include when doing a redirect from a BPF_SK_SKB_STREAM_VERDICT > program. One use case is to redirect TLS packets into a receive socket > that doesn't expect TLS data. In TLS case the first 13B or so contain the > protocol header. With KTLS the payload is decrypted so we should be able > to redirect this to a receiving socket, but the receiving socket may not > be expecting to receive a TLS header and discard the data. Using the > above helper we can pop the header off and put an appropriate header on > the payload. This allows for creating a proxy between protocols without > extra hops through the stack or userspace. > > So in order to fix this case add skb_adjust_room() so users can strip the > header. After this the user can strip the header and an unmodified receiver > thread will work correctly when data is redirected into the ingress path > of a sock. > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > --- > net/core/filter.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 51 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index 4d8dc7a31a78..d232358f1dcd 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -76,6 +76,7 @@ > #include <net/bpf_sk_storage.h> > #include <net/transp_v6.h> > #include <linux/btf_ids.h> > +#include <net/tls.h> > > static const struct bpf_func_proto * > bpf_sk_base_func_proto(enum bpf_func_id func_id); > @@ -3218,6 +3219,53 @@ static u32 __bpf_skb_max_len(const struct sk_buff *skb) > SKB_MAX_ALLOC; > } > > +BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, > + u32, mode, u64, flags) > +{ > + unsigned int len_diff_abs = abs(len_diff); small nit: u32 > + bool shrink = len_diff < 0; > + int ret = 0; > + > + if (unlikely(flags)) > + return -EINVAL; Parameter 'mode' is not used here, I guess we need to reject anything non-zero? Similarly, any interaction wrt bpf_csum_level() that was needed back then for the bpf_skb_adjust_room()? > + if (unlikely(len_diff_abs > 0xfffU)) > + return -EFAULT; > + > + if (!shrink) { > + unsigned int grow = len_diff; nit: u32 or just directly len_diff? > + ret = skb_cow(skb, grow); > + if (likely(!ret)) { > + __skb_push(skb, len_diff_abs); > + memset(skb->data, 0, len_diff_abs); > + } > + } else { > + /* skb_ensure_writable() is not needed here, as we're > + * already working on an uncloned skb. > + */ > + if (unlikely(!pskb_may_pull(skb, len_diff_abs))) > + return -ENOMEM; > + __skb_pull(skb, len_diff_abs); > + } > + bpf_compute_data_end_sk_skb(skb); > + if (tls_sw_has_ctx_rx(skb->sk)) { > + struct strp_msg *rxm = strp_msg(skb); > + > + rxm->full_len += len_diff; If skb_cow() failed, we still adjust rxm->full_len? > + } > + return ret; > +} > + > +static const struct bpf_func_proto sk_skb_adjust_room_proto = { > + .func = sk_skb_adjust_room, > + .gpl_only = false, > + .ret_type = RET_INTEGER, > + .arg1_type = ARG_PTR_TO_CTX, > + .arg2_type = ARG_ANYTHING, > + .arg3_type = ARG_ANYTHING, > + .arg4_type = ARG_ANYTHING, > +}; > + > BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, > u32, mode, u64, flags) > { > @@ -6483,6 +6531,7 @@ bool bpf_helper_changes_pkt_data(void *func) > func == bpf_skb_change_tail || > func == sk_skb_change_tail || > func == bpf_skb_adjust_room || > + func == sk_skb_adjust_room || > func == bpf_skb_pull_data || > func == sk_skb_pull_data || > func == bpf_clone_redirect || > @@ -6950,6 +6999,8 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) > return &sk_skb_change_tail_proto; > case BPF_FUNC_skb_change_head: > return &sk_skb_change_head_proto; > + case BPF_FUNC_skb_adjust_room: > + return &sk_skb_adjust_room_proto; > case BPF_FUNC_get_socket_cookie: > return &bpf_get_socket_cookie_proto; > case BPF_FUNC_get_socket_uid: >
Daniel Borkmann wrote: > On 9/26/20 6:27 AM, John Fastabend wrote: > > This implements a new helper skb_adjust_room() so users can push/pop > > extra bytes from a BPF_SK_SKB_STREAM_VERDICT program. > > > > Some protocols may include headers and other information that we may > > not want to include when doing a redirect from a BPF_SK_SKB_STREAM_VERDICT > > program. One use case is to redirect TLS packets into a receive socket > > that doesn't expect TLS data. In TLS case the first 13B or so contain the > > protocol header. With KTLS the payload is decrypted so we should be able > > to redirect this to a receiving socket, but the receiving socket may not > > be expecting to receive a TLS header and discard the data. Using the > > above helper we can pop the header off and put an appropriate header on > > the payload. This allows for creating a proxy between protocols without > > extra hops through the stack or userspace. > > > > So in order to fix this case add skb_adjust_room() so users can strip the > > header. After this the user can strip the header and an unmodified receiver > > thread will work correctly when data is redirected into the ingress path > > of a sock. > > > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > > --- > > net/core/filter.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 51 insertions(+) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 4d8dc7a31a78..d232358f1dcd 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -76,6 +76,7 @@ > > #include <net/bpf_sk_storage.h> > > #include <net/transp_v6.h> > > #include <linux/btf_ids.h> > > +#include <net/tls.h> > > > > static const struct bpf_func_proto * > > bpf_sk_base_func_proto(enum bpf_func_id func_id); > > @@ -3218,6 +3219,53 @@ static u32 __bpf_skb_max_len(const struct sk_buff *skb) > > SKB_MAX_ALLOC; > > } > > > > +BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, > > + u32, mode, u64, flags) > > +{ > > + unsigned int len_diff_abs = abs(len_diff); > > small nit: u32 Sure. > > > + bool shrink = len_diff < 0; > > + int ret = 0; > > + > > + if (unlikely(flags)) > > + return -EINVAL; > > Parameter 'mode' is not used here, I guess we need to reject anything non-zero? Probably its not used. > > Similarly, any interaction wrt bpf_csum_level() that was needed back then for the > bpf_skb_adjust_room()? I don't believe so because we are above csum checks at this point. Either we will put the skb data in the receive_queue for the socket or redirect it into sendpage. > > > + if (unlikely(len_diff_abs > 0xfffU)) > > + return -EFAULT; > > + > > + if (!shrink) { > > + unsigned int grow = len_diff; > > nit: u32 or just directly len_diff? Just use len_diff missed when I cleaned this up. > > > + ret = skb_cow(skb, grow); > > + if (likely(!ret)) { > > + __skb_push(skb, len_diff_abs); > > + memset(skb->data, 0, len_diff_abs); > > + } > > + } else { > > + /* skb_ensure_writable() is not needed here, as we're > > + * already working on an uncloned skb. > > + */ > > + if (unlikely(!pskb_may_pull(skb, len_diff_abs))) > > + return -ENOMEM; > > + __skb_pull(skb, len_diff_abs); > > + } > > + bpf_compute_data_end_sk_skb(skb); > > + if (tls_sw_has_ctx_rx(skb->sk)) { > > + struct strp_msg *rxm = strp_msg(skb); > > + > > + rxm->full_len += len_diff; > > If skb_cow() failed, we still adjust rxm->full_len? Thanks. Will just return above on error like in the else branch. I'll send a v2 shortly.
On Sat, Sep 26, 2020 at 06:27 AM CEST, John Fastabend wrote: > This implements a new helper skb_adjust_room() so users can push/pop > extra bytes from a BPF_SK_SKB_STREAM_VERDICT program. > > Some protocols may include headers and other information that we may > not want to include when doing a redirect from a BPF_SK_SKB_STREAM_VERDICT > program. One use case is to redirect TLS packets into a receive socket > that doesn't expect TLS data. In TLS case the first 13B or so contain the > protocol header. With KTLS the payload is decrypted so we should be able > to redirect this to a receiving socket, but the receiving socket may not > be expecting to receive a TLS header and discard the data. Using the > above helper we can pop the header off and put an appropriate header on > the payload. This allows for creating a proxy between protocols without > extra hops through the stack or userspace. This is useful stuff. Apart from the TLS use-case, you might want to pop off proxy headers like PROXY v1/v2 (CC Marek): https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt > > So in order to fix this case add skb_adjust_room() so users can strip the > header. After this the user can strip the header and an unmodified receiver > thread will work correctly when data is redirected into the ingress path > of a sock. > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > --- > net/core/filter.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 51 insertions(+) > > diff --git a/net/core/filter.c b/net/core/filter.c > index 4d8dc7a31a78..d232358f1dcd 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -76,6 +76,7 @@ > #include <net/bpf_sk_storage.h> > #include <net/transp_v6.h> > #include <linux/btf_ids.h> > +#include <net/tls.h> > > static const struct bpf_func_proto * > bpf_sk_base_func_proto(enum bpf_func_id func_id); > @@ -3218,6 +3219,53 @@ static u32 __bpf_skb_max_len(const struct sk_buff *skb) > SKB_MAX_ALLOC; > } > > +BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, > + u32, mode, u64, flags) > +{ > + unsigned int len_diff_abs = abs(len_diff); > + bool shrink = len_diff < 0; > + int ret = 0; > + > + if (unlikely(flags)) > + return -EINVAL; > + if (unlikely(len_diff_abs > 0xfffU)) > + return -EFAULT; > + > + if (!shrink) { > + unsigned int grow = len_diff; > + > + ret = skb_cow(skb, grow); > + if (likely(!ret)) { > + __skb_push(skb, len_diff_abs); > + memset(skb->data, 0, len_diff_abs); > + } > + } else { > + /* skb_ensure_writable() is not needed here, as we're > + * already working on an uncloned skb. > + */ I'm trying to digest the above comment. What if: static int __strp_recv(…) { … while (eaten < orig_len) { /* Always clone since we will consume something */ skb = skb_clone(orig_skb, GFP_ATOMIC); … head = strp->skb_head; if (!head) { head = skb; … } else { … } … /* Give skb to upper layer */ strp->cb.rcv_msg(strp, head); // → sk_psock_init_strp … } … } That looks like a code path where we pass a cloned SKB. > + if (unlikely(!pskb_may_pull(skb, len_diff_abs))) > + return -ENOMEM; > + __skb_pull(skb, len_diff_abs); > + } > + bpf_compute_data_end_sk_skb(skb); > + if (tls_sw_has_ctx_rx(skb->sk)) { > + struct strp_msg *rxm = strp_msg(skb); > + > + rxm->full_len += len_diff; > + } > + return ret; > +} [...]
Jakub Sitnicki wrote: > On Sat, Sep 26, 2020 at 06:27 AM CEST, John Fastabend wrote: > > This implements a new helper skb_adjust_room() so users can push/pop > > extra bytes from a BPF_SK_SKB_STREAM_VERDICT program. > > > > Some protocols may include headers and other information that we may > > not want to include when doing a redirect from a BPF_SK_SKB_STREAM_VERDICT > > program. One use case is to redirect TLS packets into a receive socket > > that doesn't expect TLS data. In TLS case the first 13B or so contain the > > protocol header. With KTLS the payload is decrypted so we should be able > > to redirect this to a receiving socket, but the receiving socket may not > > be expecting to receive a TLS header and discard the data. Using the > > above helper we can pop the header off and put an appropriate header on > > the payload. This allows for creating a proxy between protocols without > > extra hops through the stack or userspace. > > This is useful stuff. Apart from the TLS use-case, you might want to pop > off proxy headers like PROXY v1/v2 (CC Marek): > > https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt Great! > > > > > So in order to fix this case add skb_adjust_room() so users can strip the > > header. After this the user can strip the header and an unmodified receiver > > thread will work correctly when data is redirected into the ingress path > > of a sock. > > > > Signed-off-by: John Fastabend <john.fastabend@gmail.com> > > --- > > net/core/filter.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 51 insertions(+) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 4d8dc7a31a78..d232358f1dcd 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -76,6 +76,7 @@ > > #include <net/bpf_sk_storage.h> > > #include <net/transp_v6.h> > > #include <linux/btf_ids.h> > > +#include <net/tls.h> > > > > static const struct bpf_func_proto * > > bpf_sk_base_func_proto(enum bpf_func_id func_id); > > @@ -3218,6 +3219,53 @@ static u32 __bpf_skb_max_len(const struct sk_buff *skb) > > SKB_MAX_ALLOC; > > } > > > > +BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, > > + u32, mode, u64, flags) > > +{ > > + unsigned int len_diff_abs = abs(len_diff); > > + bool shrink = len_diff < 0; > > + int ret = 0; > > + > > + if (unlikely(flags)) > > + return -EINVAL; > > + if (unlikely(len_diff_abs > 0xfffU)) > > + return -EFAULT; > > + > > + if (!shrink) { > > + unsigned int grow = len_diff; > > + > > + ret = skb_cow(skb, grow); > > + if (likely(!ret)) { > > + __skb_push(skb, len_diff_abs); > > + memset(skb->data, 0, len_diff_abs); > > + } > > + } else { > > + /* skb_ensure_writable() is not needed here, as we're > > + * already working on an uncloned skb. > > + */ > > I'm trying to digest the above comment. What if: I'll delete the comment its not accurate. We happily write headers from verdict programs today. Do you have a specific concern or just noticing I was a bit careless and cut'n'pasted an incorrect comment around. > > static int __strp_recv(…) > { > … > while (eaten < orig_len) { > /* Always clone since we will consume something */ > skb = skb_clone(orig_skb, GFP_ATOMIC); > … > head = strp->skb_head; > if (!head) { > head = skb; > … > } else { > … > } > … > /* Give skb to upper layer */ > strp->cb.rcv_msg(strp, head); // → sk_psock_init_strp > … > } > … > } > > That looks like a code path where we pass a cloned SKB. Right but its there to cover the sk_eat_skb in tcp_read_sock() otherwise sk_eat_skb() -> __kfree_skb() -> skb_release_all() would go all the way to page_frag_free(). > > > + if (unlikely(!pskb_may_pull(skb, len_diff_abs))) > > + return -ENOMEM; > > + __skb_pull(skb, len_diff_abs); > > + } > > + bpf_compute_data_end_sk_skb(skb); > > + if (tls_sw_has_ctx_rx(skb->sk)) { > > + struct strp_msg *rxm = strp_msg(skb); > > + > > + rxm->full_len += len_diff; > > + } > > + return ret; > > +} > > [...]
diff --git a/net/core/filter.c b/net/core/filter.c index 4d8dc7a31a78..d232358f1dcd 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -76,6 +76,7 @@ #include <net/bpf_sk_storage.h> #include <net/transp_v6.h> #include <linux/btf_ids.h> +#include <net/tls.h> static const struct bpf_func_proto * bpf_sk_base_func_proto(enum bpf_func_id func_id); @@ -3218,6 +3219,53 @@ static u32 __bpf_skb_max_len(const struct sk_buff *skb) SKB_MAX_ALLOC; } +BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, + u32, mode, u64, flags) +{ + unsigned int len_diff_abs = abs(len_diff); + bool shrink = len_diff < 0; + int ret = 0; + + if (unlikely(flags)) + return -EINVAL; + if (unlikely(len_diff_abs > 0xfffU)) + return -EFAULT; + + if (!shrink) { + unsigned int grow = len_diff; + + ret = skb_cow(skb, grow); + if (likely(!ret)) { + __skb_push(skb, len_diff_abs); + memset(skb->data, 0, len_diff_abs); + } + } else { + /* skb_ensure_writable() is not needed here, as we're + * already working on an uncloned skb. + */ + if (unlikely(!pskb_may_pull(skb, len_diff_abs))) + return -ENOMEM; + __skb_pull(skb, len_diff_abs); + } + bpf_compute_data_end_sk_skb(skb); + if (tls_sw_has_ctx_rx(skb->sk)) { + struct strp_msg *rxm = strp_msg(skb); + + rxm->full_len += len_diff; + } + return ret; +} + +static const struct bpf_func_proto sk_skb_adjust_room_proto = { + .func = sk_skb_adjust_room, + .gpl_only = false, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_CTX, + .arg2_type = ARG_ANYTHING, + .arg3_type = ARG_ANYTHING, + .arg4_type = ARG_ANYTHING, +}; + BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, u32, mode, u64, flags) { @@ -6483,6 +6531,7 @@ bool bpf_helper_changes_pkt_data(void *func) func == bpf_skb_change_tail || func == sk_skb_change_tail || func == bpf_skb_adjust_room || + func == sk_skb_adjust_room || func == bpf_skb_pull_data || func == sk_skb_pull_data || func == bpf_clone_redirect || @@ -6950,6 +6999,8 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &sk_skb_change_tail_proto; case BPF_FUNC_skb_change_head: return &sk_skb_change_head_proto; + case BPF_FUNC_skb_adjust_room: + return &sk_skb_adjust_room_proto; case BPF_FUNC_get_socket_cookie: return &bpf_get_socket_cookie_proto; case BPF_FUNC_get_socket_uid:
This implements a new helper skb_adjust_room() so users can push/pop extra bytes from a BPF_SK_SKB_STREAM_VERDICT program. Some protocols may include headers and other information that we may not want to include when doing a redirect from a BPF_SK_SKB_STREAM_VERDICT program. One use case is to redirect TLS packets into a receive socket that doesn't expect TLS data. In TLS case the first 13B or so contain the protocol header. With KTLS the payload is decrypted so we should be able to redirect this to a receiving socket, but the receiving socket may not be expecting to receive a TLS header and discard the data. Using the above helper we can pop the header off and put an appropriate header on the payload. This allows for creating a proxy between protocols without extra hops through the stack or userspace. So in order to fix this case add skb_adjust_room() so users can strip the header. After this the user can strip the header and an unmodified receiver thread will work correctly when data is redirected into the ingress path of a sock. Signed-off-by: John Fastabend <john.fastabend@gmail.com> --- net/core/filter.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+)