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bpf: allow sk_msg programs to read sock fields
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Currently sk_msg programs only have access to the raw data. However,
it is often useful when building policies to have the policies specific
to the socket endpoint. This allows using the socket tuple as input
into filters, etc.

This patch adds ctx access to the sock fields.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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John Fastabend authored and Daniel Borkmann committed May 18, 2018
1 parent 1cb6138 commit 303def3
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Showing 4 changed files with 121 additions and 3 deletions.
1 change: 1 addition & 0 deletions include/linux/filter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -517,6 +517,7 @@ struct sk_msg_buff {
bool sg_copy[MAX_SKB_FRAGS];
__u32 flags;
struct sock *sk_redir;
struct sock *sk;
struct sk_buff *skb;
struct list_head list;
};
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8 changes: 8 additions & 0 deletions include/uapi/linux/bpf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2176,6 +2176,14 @@ enum sk_action {
struct sk_msg_md {
void *data;
void *data_end;

__u32 family;
__u32 remote_ip4; /* Stored in network byte order */
__u32 local_ip4; /* Stored in network byte order */
__u32 remote_ip6[4]; /* Stored in network byte order */
__u32 local_ip6[4]; /* Stored in network byte order */
__u32 remote_port; /* Stored in network byte order */
__u32 local_port; /* stored in host byte order */
};

#define BPF_TAG_SIZE 8
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1 change: 1 addition & 0 deletions kernel/bpf/sockmap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -523,6 +523,7 @@ static unsigned int smap_do_tx_msg(struct sock *sk,
}

bpf_compute_data_pointers_sg(md);
md->sk = sk;
rc = (*prog->bpf_func)(md, prog->insnsi);
psock->apply_bytes = md->apply_bytes;

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114 changes: 111 additions & 3 deletions net/core/filter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5148,18 +5148,23 @@ static bool sk_msg_is_valid_access(int off, int size,
switch (off) {
case offsetof(struct sk_msg_md, data):
info->reg_type = PTR_TO_PACKET;
if (size != sizeof(__u64))
return false;
break;
case offsetof(struct sk_msg_md, data_end):
info->reg_type = PTR_TO_PACKET_END;
if (size != sizeof(__u64))
return false;
break;
default:
if (size != sizeof(__u32))
return false;
}

if (off < 0 || off >= sizeof(struct sk_msg_md))
return false;
if (off % size != 0)
return false;
if (size != sizeof(__u64))
return false;

return true;
}
Expand Down Expand Up @@ -5835,7 +5840,8 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
break;

case offsetof(struct bpf_sock_ops, local_ip4):
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common, skc_rcv_saddr) != 4);
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common,
skc_rcv_saddr) != 4);

*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct bpf_sock_ops_kern, sk),
Expand Down Expand Up @@ -6152,6 +6158,7 @@ static u32 sk_msg_convert_ctx_access(enum bpf_access_type type,
struct bpf_prog *prog, u32 *target_size)
{
struct bpf_insn *insn = insn_buf;
int off;

switch (si->off) {
case offsetof(struct sk_msg_md, data):
Expand All @@ -6164,6 +6171,107 @@ static u32 sk_msg_convert_ctx_access(enum bpf_access_type type,
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, data_end));
break;
case offsetof(struct sk_msg_md, family):
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common, skc_family) != 2);

*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->dst_reg,
offsetof(struct sock_common, skc_family));
break;

case offsetof(struct sk_msg_md, remote_ip4):
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common, skc_daddr) != 4);

*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
offsetof(struct sock_common, skc_daddr));
break;

case offsetof(struct sk_msg_md, local_ip4):
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common,
skc_rcv_saddr) != 4);

*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
offsetof(struct sock_common,
skc_rcv_saddr));
break;

case offsetof(struct sk_msg_md, remote_ip6[0]) ...
offsetof(struct sk_msg_md, remote_ip6[3]):
#if IS_ENABLED(CONFIG_IPV6)
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common,
skc_v6_daddr.s6_addr32[0]) != 4);

off = si->off;
off -= offsetof(struct sk_msg_md, remote_ip6[0]);
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
offsetof(struct sock_common,
skc_v6_daddr.s6_addr32[0]) +
off);
#else
*insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
#endif
break;

case offsetof(struct sk_msg_md, local_ip6[0]) ...
offsetof(struct sk_msg_md, local_ip6[3]):
#if IS_ENABLED(CONFIG_IPV6)
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common,
skc_v6_rcv_saddr.s6_addr32[0]) != 4);

off = si->off;
off -= offsetof(struct sk_msg_md, local_ip6[0]);
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,
offsetof(struct sock_common,
skc_v6_rcv_saddr.s6_addr32[0]) +
off);
#else
*insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
#endif
break;

case offsetof(struct sk_msg_md, remote_port):
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common, skc_dport) != 2);

*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->dst_reg,
offsetof(struct sock_common, skc_dport));
#ifndef __BIG_ENDIAN_BITFIELD
*insn++ = BPF_ALU32_IMM(BPF_LSH, si->dst_reg, 16);
#endif
break;

case offsetof(struct sk_msg_md, local_port):
BUILD_BUG_ON(FIELD_SIZEOF(struct sock_common, skc_num) != 2);

*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
struct sk_msg_buff, sk),
si->dst_reg, si->src_reg,
offsetof(struct sk_msg_buff, sk));
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->dst_reg,
offsetof(struct sock_common, skc_num));
break;
}

return insn - insn_buf;
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