On 1/9/18, 3:22 PM, "[email protected] on behalf of Eric Dumazet"
<[email protected] on behalf of [email protected]> wrote:
On Tue, 2018-01-09 at 13:06 -0800, Lawrence Brakmo wrote:
> This patch adds a macro, SOCK_OPS_SET_FIELD, for writing to
> struct tcp_sock or struct sock fields. This required adding a new
> field "temp" to struct bpf_sock_ops_kern for temporary storage that
> is used by sock_ops_convert_ctx_access. It is used to store and recover
> the contents of a register, so the register can be used to store the
> address of the sk. Since we cannot overwrite the dst_reg because it
> contains the pointer to ctx, nor the src_reg since it contains the value
> we want to store, we need an extra register to contain the address
> of the sk.
>
> Also adds the macro SOCK_OPS_GET_OR_SET_FIELD that calls one of the
> GET or SET macros depending on the value of the TYPE field.
>
> Signed-off-by: Lawrence Brakmo <[email protected]>
> ---
> include/linux/filter.h | 3 +++
> include/net/tcp.h | 2 +-
> net/core/filter.c | 48
++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 425056c..139a9a3 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1007,6 +1007,9 @@ struct bpf_sock_ops_kern {
> u32 replylong[4];
> };
> u32 is_fullsock;
> + u64 temp; /* Used by sock_ops_convert_ctx_access
> + * as temporary storaage of a register
typo on storage
Thanks, will fix.
> + */
> };
>
> #endif /* __LINUX_FILTER_H__ */
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 6939e69..108d16a 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2010,7 +2010,7 @@ static inline int tcp_call_bpf(struct sock *sk, int
op)
> struct bpf_sock_ops_kern sock_ops;
> int ret;
>
> - memset(&sock_ops, 0, sizeof(sock_ops));
> + memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
>
This lacks proper comment, stating that every field added after .temp
in struct bpf_sock_ops_kern is considered as scratch and could contain
garbage.
I assumed that one would modify this initialization appropriately when adding
a new field. But it would certainly make sense to indicate that new,
non-scratch,
fields should be added before temp so there would be no need to modify this
initialization code. Makes sense?
