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bpf: allow programs to write to certain skb fields
allow programs read/write skb->mark, tc_index fields and ((struct qdisc_skb_cb *)cb)->data. mark and tc_index are generically useful in TC. cb[0]-cb[4] are primarily used to pass arguments from one program to another called via bpf_tail_call() which can be seen in sockex3_kern.c example. All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs. mark, tc_index are writeable from tc_cls_act only. cb[0]-cb[4] are writeable by both sockets and tc_cls_act. Add verifier tests and improve sample code. Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov
David S. Miller
parent
3431205e03
commit
d691f9e8d4
6 changed files with 207 additions and 48 deletions
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@ -105,7 +105,8 @@ struct bpf_verifier_ops {
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*/
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bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
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u32 (*convert_ctx_access)(int dst_reg, int src_reg, int ctx_off,
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u32 (*convert_ctx_access)(enum bpf_access_type type, int dst_reg,
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int src_reg, int ctx_off,
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struct bpf_insn *insn);
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};
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@ -248,6 +248,8 @@ struct __sk_buff {
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__u32 priority;
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__u32 ingress_ifindex;
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__u32 ifindex;
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__u32 tc_index;
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__u32 cb[5];
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};
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#endif /* _UAPI__LINUX_BPF_H__ */
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@ -1692,6 +1692,8 @@ static int do_check(struct verifier_env *env)
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}
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} else if (class == BPF_STX) {
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enum bpf_reg_type dst_reg_type;
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if (BPF_MODE(insn->code) == BPF_XADD) {
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err = check_xadd(env, insn);
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if (err)
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@ -1700,11 +1702,6 @@ static int do_check(struct verifier_env *env)
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continue;
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}
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if (BPF_MODE(insn->code) != BPF_MEM ||
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insn->imm != 0) {
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verbose("BPF_STX uses reserved fields\n");
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return -EINVAL;
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}
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/* check src1 operand */
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err = check_reg_arg(regs, insn->src_reg, SRC_OP);
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if (err)
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@ -1714,6 +1711,8 @@ static int do_check(struct verifier_env *env)
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if (err)
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return err;
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dst_reg_type = regs[insn->dst_reg].type;
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/* check that memory (dst_reg + off) is writeable */
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err = check_mem_access(env, insn->dst_reg, insn->off,
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BPF_SIZE(insn->code), BPF_WRITE,
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@ -1721,6 +1720,15 @@ static int do_check(struct verifier_env *env)
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if (err)
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return err;
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if (insn->imm == 0) {
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insn->imm = dst_reg_type;
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} else if (dst_reg_type != insn->imm &&
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(dst_reg_type == PTR_TO_CTX ||
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insn->imm == PTR_TO_CTX)) {
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verbose("same insn cannot be used with different pointers\n");
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return -EINVAL;
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}
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} else if (class == BPF_ST) {
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if (BPF_MODE(insn->code) != BPF_MEM ||
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insn->src_reg != BPF_REG_0) {
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@ -1839,12 +1847,18 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env)
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for (i = 0; i < insn_cnt; i++, insn++) {
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if (BPF_CLASS(insn->code) == BPF_LDX &&
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(BPF_MODE(insn->code) != BPF_MEM ||
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insn->imm != 0)) {
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(BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
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verbose("BPF_LDX uses reserved fields\n");
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return -EINVAL;
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}
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if (BPF_CLASS(insn->code) == BPF_STX &&
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((BPF_MODE(insn->code) != BPF_MEM &&
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BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
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verbose("BPF_STX uses reserved fields\n");
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return -EINVAL;
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}
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if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
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struct bpf_map *map;
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struct fd f;
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@ -1967,12 +1981,17 @@ static int convert_ctx_accesses(struct verifier_env *env)
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struct bpf_prog *new_prog;
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u32 cnt;
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int i;
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enum bpf_access_type type;
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if (!env->prog->aux->ops->convert_ctx_access)
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return 0;
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for (i = 0; i < insn_cnt; i++, insn++) {
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if (insn->code != (BPF_LDX | BPF_MEM | BPF_W))
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if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
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type = BPF_READ;
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else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
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type = BPF_WRITE;
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else
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continue;
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if (insn->imm != PTR_TO_CTX) {
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@ -1982,7 +2001,7 @@ static int convert_ctx_accesses(struct verifier_env *env)
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}
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cnt = env->prog->aux->ops->
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convert_ctx_access(insn->dst_reg, insn->src_reg,
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convert_ctx_access(type, insn->dst_reg, insn->src_reg,
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insn->off, insn_buf);
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if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
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verbose("bpf verifier is misconfigured\n");
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@ -46,6 +46,7 @@
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#include <linux/seccomp.h>
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#include <linux/if_vlan.h>
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#include <linux/bpf.h>
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#include <net/sch_generic.h>
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/**
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* sk_filter - run a packet through a socket filter
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@ -1463,13 +1464,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
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}
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}
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static bool sk_filter_is_valid_access(int off, int size,
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enum bpf_access_type type)
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static bool __is_valid_access(int off, int size, enum bpf_access_type type)
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{
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/* only read is allowed */
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if (type != BPF_READ)
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return false;
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/* check bounds */
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if (off < 0 || off >= sizeof(struct __sk_buff))
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return false;
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@ -1485,8 +1481,42 @@ static bool sk_filter_is_valid_access(int off, int size,
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return true;
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}
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static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
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struct bpf_insn *insn_buf)
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static bool sk_filter_is_valid_access(int off, int size,
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enum bpf_access_type type)
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{
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if (type == BPF_WRITE) {
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switch (off) {
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case offsetof(struct __sk_buff, cb[0]) ...
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offsetof(struct __sk_buff, cb[4]):
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break;
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default:
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return false;
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}
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}
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return __is_valid_access(off, size, type);
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}
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static bool tc_cls_act_is_valid_access(int off, int size,
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enum bpf_access_type type)
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{
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if (type == BPF_WRITE) {
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switch (off) {
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case offsetof(struct __sk_buff, mark):
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case offsetof(struct __sk_buff, tc_index):
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case offsetof(struct __sk_buff, cb[0]) ...
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offsetof(struct __sk_buff, cb[4]):
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break;
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default:
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return false;
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}
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}
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return __is_valid_access(off, size, type);
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}
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static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
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int src_reg, int ctx_off,
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struct bpf_insn *insn_buf)
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{
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struct bpf_insn *insn = insn_buf;
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@ -1538,7 +1568,15 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
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break;
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case offsetof(struct __sk_buff, mark):
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return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn);
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BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
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if (type == BPF_WRITE)
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*insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg,
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offsetof(struct sk_buff, mark));
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else
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*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
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offsetof(struct sk_buff, mark));
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break;
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case offsetof(struct __sk_buff, pkt_type):
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return convert_skb_access(SKF_AD_PKTTYPE, dst_reg, src_reg, insn);
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@ -1553,6 +1591,38 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
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case offsetof(struct __sk_buff, vlan_tci):
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return convert_skb_access(SKF_AD_VLAN_TAG,
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dst_reg, src_reg, insn);
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case offsetof(struct __sk_buff, cb[0]) ...
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offsetof(struct __sk_buff, cb[4]):
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BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, data) < 20);
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ctx_off -= offsetof(struct __sk_buff, cb[0]);
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ctx_off += offsetof(struct sk_buff, cb);
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ctx_off += offsetof(struct qdisc_skb_cb, data);
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if (type == BPF_WRITE)
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*insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg, ctx_off);
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else
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*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg, ctx_off);
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break;
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case offsetof(struct __sk_buff, tc_index):
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#ifdef CONFIG_NET_SCHED
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BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, tc_index) != 2);
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if (type == BPF_WRITE)
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*insn++ = BPF_STX_MEM(BPF_H, dst_reg, src_reg,
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offsetof(struct sk_buff, tc_index));
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else
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*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
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offsetof(struct sk_buff, tc_index));
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break;
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#else
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if (type == BPF_WRITE)
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*insn++ = BPF_MOV64_REG(dst_reg, dst_reg);
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else
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*insn++ = BPF_MOV64_IMM(dst_reg, 0);
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break;
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#endif
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}
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return insn - insn_buf;
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@ -1561,13 +1631,13 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
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static const struct bpf_verifier_ops sk_filter_ops = {
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.get_func_proto = sk_filter_func_proto,
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.is_valid_access = sk_filter_is_valid_access,
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.convert_ctx_access = sk_filter_convert_ctx_access,
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.convert_ctx_access = bpf_net_convert_ctx_access,
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};
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static const struct bpf_verifier_ops tc_cls_act_ops = {
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.get_func_proto = tc_cls_act_func_proto,
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.is_valid_access = sk_filter_is_valid_access,
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.convert_ctx_access = sk_filter_convert_ctx_access,
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.is_valid_access = tc_cls_act_is_valid_access,
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.convert_ctx_access = bpf_net_convert_ctx_access,
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};
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static struct bpf_prog_type_list sk_filter_type __read_mostly = {
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@ -89,7 +89,6 @@ static inline __u32 ipv6_addr_hash(struct __sk_buff *ctx, __u64 off)
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struct globals {
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struct flow_keys flow;
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__u32 nhoff;
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};
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struct bpf_map_def SEC("maps") percpu_map = {
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@ -139,7 +138,7 @@ static void update_stats(struct __sk_buff *skb, struct globals *g)
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static __always_inline void parse_ip_proto(struct __sk_buff *skb,
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struct globals *g, __u32 ip_proto)
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{
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__u32 nhoff = g->nhoff;
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__u32 nhoff = skb->cb[0];
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int poff;
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switch (ip_proto) {
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@ -165,7 +164,7 @@ static __always_inline void parse_ip_proto(struct __sk_buff *skb,
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if (gre_flags & GRE_SEQ)
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nhoff += 4;
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g->nhoff = nhoff;
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skb->cb[0] = nhoff;
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parse_eth_proto(skb, gre_proto);
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break;
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}
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@ -195,7 +194,7 @@ PROG(PARSE_IP)(struct __sk_buff *skb)
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if (!g)
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return 0;
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nhoff = g->nhoff;
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nhoff = skb->cb[0];
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if (unlikely(ip_is_fragment(skb, nhoff)))
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return 0;
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@ -210,7 +209,7 @@ PROG(PARSE_IP)(struct __sk_buff *skb)
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verlen = load_byte(skb, nhoff + 0/*offsetof(struct iphdr, ihl)*/);
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nhoff += (verlen & 0xF) << 2;
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g->nhoff = nhoff;
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skb->cb[0] = nhoff;
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parse_ip_proto(skb, g, ip_proto);
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return 0;
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}
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@ -223,7 +222,7 @@ PROG(PARSE_IPV6)(struct __sk_buff *skb)
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if (!g)
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return 0;
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nhoff = g->nhoff;
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nhoff = skb->cb[0];
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ip_proto = load_byte(skb,
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nhoff + offsetof(struct ipv6hdr, nexthdr));
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@ -233,25 +232,21 @@ PROG(PARSE_IPV6)(struct __sk_buff *skb)
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nhoff + offsetof(struct ipv6hdr, daddr));
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nhoff += sizeof(struct ipv6hdr);
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g->nhoff = nhoff;
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skb->cb[0] = nhoff;
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parse_ip_proto(skb, g, ip_proto);
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return 0;
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}
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PROG(PARSE_VLAN)(struct __sk_buff *skb)
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{
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struct globals *g = this_cpu_globals();
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__u32 nhoff, proto;
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if (!g)
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return 0;
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nhoff = g->nhoff;
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nhoff = skb->cb[0];
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proto = load_half(skb, nhoff + offsetof(struct vlan_hdr,
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h_vlan_encapsulated_proto));
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nhoff += sizeof(struct vlan_hdr);
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g->nhoff = nhoff;
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skb->cb[0] = nhoff;
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parse_eth_proto(skb, proto);
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@ -260,17 +255,13 @@ PROG(PARSE_VLAN)(struct __sk_buff *skb)
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PROG(PARSE_MPLS)(struct __sk_buff *skb)
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{
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struct globals *g = this_cpu_globals();
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__u32 nhoff, label;
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if (!g)
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return 0;
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nhoff = g->nhoff;
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nhoff = skb->cb[0];
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label = load_word(skb, nhoff);
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nhoff += sizeof(struct mpls_label);
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g->nhoff = nhoff;
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skb->cb[0] = nhoff;
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if (label & MPLS_LS_S_MASK) {
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__u8 verlen = load_byte(skb, nhoff);
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@ -288,14 +279,10 @@ PROG(PARSE_MPLS)(struct __sk_buff *skb)
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SEC("socket/0")
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int main_prog(struct __sk_buff *skb)
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{
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struct globals *g = this_cpu_globals();
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__u32 nhoff = ETH_HLEN;
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__u32 proto = load_half(skb, 12);
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if (!g)
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return 0;
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g->nhoff = nhoff;
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skb->cb[0] = nhoff;
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parse_eth_proto(skb, proto);
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return 0;
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}
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@ -29,6 +29,7 @@ struct bpf_test {
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ACCEPT,
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REJECT
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} result;
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enum bpf_prog_type prog_type;
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};
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static struct bpf_test tests[] = {
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@ -743,6 +744,84 @@ static struct bpf_test tests[] = {
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.errstr = "different pointers",
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.result = REJECT,
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},
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{
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"check skb->mark is not writeable by sockets",
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.insns = {
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BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
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offsetof(struct __sk_buff, mark)),
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BPF_EXIT_INSN(),
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},
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.errstr = "invalid bpf_context access",
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.result = REJECT,
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},
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{
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"check skb->tc_index is not writeable by sockets",
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.insns = {
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BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
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offsetof(struct __sk_buff, tc_index)),
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BPF_EXIT_INSN(),
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},
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.errstr = "invalid bpf_context access",
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.result = REJECT,
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},
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{
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"check non-u32 access to cb",
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.insns = {
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BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_1,
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offsetof(struct __sk_buff, cb[0])),
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BPF_EXIT_INSN(),
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},
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.errstr = "invalid bpf_context access",
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.result = REJECT,
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},
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{
|
||||
"check out of range skb->cb access",
|
||||
.insns = {
|
||||
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, cb[60])),
|
||||
BPF_EXIT_INSN(),
|
||||
},
|
||||
.errstr = "invalid bpf_context access",
|
||||
.result = REJECT,
|
||||
.prog_type = BPF_PROG_TYPE_SCHED_ACT,
|
||||
},
|
||||
{
|
||||
"write skb fields from socket prog",
|
||||
.insns = {
|
||||
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, cb[4])),
|
||||
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 1),
|
||||
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, mark)),
|
||||
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, tc_index)),
|
||||
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 1),
|
||||
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, cb[0])),
|
||||
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, cb[2])),
|
||||
BPF_EXIT_INSN(),
|
||||
},
|
||||
.result = ACCEPT,
|
||||
},
|
||||
{
|
||||
"write skb fields from tc_cls_act prog",
|
||||
.insns = {
|
||||
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, cb[0])),
|
||||
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
|
||||
offsetof(struct __sk_buff, mark)),
|
||||
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
|
||||
offsetof(struct __sk_buff, tc_index)),
|
||||
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
|
||||
offsetof(struct __sk_buff, tc_index)),
|
||||
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
|
||||
offsetof(struct __sk_buff, cb[3])),
|
||||
BPF_EXIT_INSN(),
|
||||
},
|
||||
.result = ACCEPT,
|
||||
.prog_type = BPF_PROG_TYPE_SCHED_CLS,
|
||||
},
|
||||
};
|
||||
|
||||
static int probe_filter_length(struct bpf_insn *fp)
|
||||
|
|
@ -775,6 +854,7 @@ static int test(void)
|
|||
|
||||
for (i = 0; i < ARRAY_SIZE(tests); i++) {
|
||||
struct bpf_insn *prog = tests[i].insns;
|
||||
int prog_type = tests[i].prog_type;
|
||||
int prog_len = probe_filter_length(prog);
|
||||
int *fixup = tests[i].fixup;
|
||||
int map_fd = -1;
|
||||
|
|
@ -789,8 +869,8 @@ static int test(void)
|
|||
}
|
||||
printf("#%d %s ", i, tests[i].descr);
|
||||
|
||||
prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
|
||||
prog_len * sizeof(struct bpf_insn),
|
||||
prog_fd = bpf_prog_load(prog_type ?: BPF_PROG_TYPE_SOCKET_FILTER,
|
||||
prog, prog_len * sizeof(struct bpf_insn),
|
||||
"GPL", 0);
|
||||
|
||||
if (tests[i].result == ACCEPT) {
|
||||
|
|
|
|||
Loading…
Reference in a new issue