On Wed, 20 Mar 2019, Willem de Bruijn wrote:
> From: Willem de Bruijn <will...@google.com>
>
> bpf_skb_adjust_room adjusts gso_size of gso packets to account for the
> pushed or popped header room.
>
> This is not allowed with UDP, where gso_size delineates datagrams. Add
> an option to avoid these updates and allow this call for datagrams.
>
> It can also be used with TCP, when MSS is known to allow headroom,
> e.g., through MSS clamping or route MTU.
>
> Link: https://patchwork.ozlabs.org/patch/1052497/
> Signed-off-by: Willem de Bruijn <will...@google.com>
> ---
> include/uapi/linux/bpf.h | 4 ++++
> net/core/filter.c | 36 +++++++++++++++++++++++++-----------
> 2 files changed, 29 insertions(+), 11 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4f5c918e6fcf4..0eda8f564a381 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2593,6 +2593,10 @@ enum bpf_func_id {
> /* Current network namespace */
> #define BPF_F_CURRENT_NETNS (-1L)
>
> +/* BPF_FUNC_skb_adjust_room flags. */
> +#define BPF_F_ADJ_ROOM_FIXED_GSO (1ULL << 0)
minor nit - could we add this flag to the documentation for
bpf_skb_adjust_room? Same suggestion for the encap flags in
patch 8 too. Thanks!
Reviewed-by: Alan Maguire <alan.magu...@oracle.com>
> +#define BPF_F_ADJ_ROOM_MASK (BPF_F_ADJ_ROOM_FIXED_GSO)
> +
> /* Mode for BPF_FUNC_skb_adjust_room helper. */
> enum bpf_adj_room_mode {
> BPF_ADJ_ROOM_NET,
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 1a0cf578b4502..e346e48098000 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2963,12 +2963,17 @@ static u32 bpf_skb_net_base_len(const struct sk_buff
> *skb)
> }
> }
>
> -static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff)
> +static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> + u64 flags)
> {
> int ret;
>
> - if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
> - return -ENOTSUPP;
> + if (skb_is_gso(skb) && !skb_is_gso_tcp(skb)) {
> + /* udp gso_size delineates datagrams, only allow if fixed */
> + if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) ||
> + !(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
> + return -ENOTSUPP;
> + }
>
> ret = skb_cow_head(skb, len_diff);
> if (unlikely(ret < 0))
> @@ -2982,7 +2987,9 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32
> off, u32 len_diff)
> struct skb_shared_info *shinfo = skb_shinfo(skb);
>
> /* Due to header grow, MSS needs to be downgraded. */
> - skb_decrease_gso_size(shinfo, len_diff);
> + if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
> + skb_decrease_gso_size(shinfo, len_diff);
> +
> /* Header must be checked, and gso_segs recomputed. */
> shinfo->gso_type |= SKB_GSO_DODGY;
> shinfo->gso_segs = 0;
> @@ -2991,12 +2998,17 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32
> off, u32 len_diff)
> return 0;
> }
>
> -static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff)
> +static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff,
> + u64 flags)
> {
> int ret;
>
> - if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
> - return -ENOTSUPP;
> + if (skb_is_gso(skb) && !skb_is_gso_tcp(skb)) {
> + /* udp gso_size delineates datagrams, only allow if fixed */
> + if (!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) ||
> + !(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
> + return -ENOTSUPP;
> + }
>
> ret = skb_unclone(skb, GFP_ATOMIC);
> if (unlikely(ret < 0))
> @@ -3010,7 +3022,9 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32
> off, u32 len_diff)
> struct skb_shared_info *shinfo = skb_shinfo(skb);
>
> /* Due to header shrink, MSS can be upgraded. */
> - skb_increase_gso_size(shinfo, len_diff);
> + if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
> + skb_increase_gso_size(shinfo, len_diff);
> +
> /* Header must be checked, and gso_segs recomputed. */
> shinfo->gso_type |= SKB_GSO_DODGY;
> shinfo->gso_segs = 0;
> @@ -3037,7 +3051,7 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb,
> s32, len_diff,
> u32 off;
> int ret;
>
> - if (unlikely(flags))
> + if (unlikely(flags & ~BPF_F_ADJ_ROOM_MASK))
> return -EINVAL;
> if (unlikely(len_diff_abs > 0xfffU))
> return -EFAULT;
> @@ -3065,8 +3079,8 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb,
> s32, len_diff,
> !skb_is_gso(skb))))
> return -ENOTSUPP;
>
> - ret = shrink ? bpf_skb_net_shrink(skb, off, len_diff_abs) :
> - bpf_skb_net_grow(skb, off, len_diff_abs);
> + ret = shrink ? bpf_skb_net_shrink(skb, off, len_diff_abs, flags) :
> + bpf_skb_net_grow(skb, off, len_diff_abs, flags);
>
> bpf_compute_data_pointers(skb);
> return ret;
> --
> 2.21.0.225.g810b269d1ac-goog
>
>
