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bpf: allow programs to write to certain skb fields

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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
2015-06-07 02:01:33 -07:00
committed by David S. Miller
parent 3431205e03
commit d691f9e8d4
6 changed files with 207 additions and 48 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/bpf/verifier.c
+28 -9
View File
@@ -1692,6 +1692,8 @@ static int do_check(struct verifier_env *env)
}
} else if (class == BPF_STX) {
enum bpf_reg_type dst_reg_type;
if (BPF_MODE(insn->code) == BPF_XADD) {
err = check_xadd(env, insn);
if (err)
@@ -1700,11 +1702,6 @@ static int do_check(struct verifier_env *env)
continue;
}
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->imm != 0) {
verbose("BPF_STX uses reserved fields\n");
return -EINVAL;
}
/* check src1 operand */
err = check_reg_arg(regs, insn->src_reg, SRC_OP);
if (err)
@@ -1714,6 +1711,8 @@ static int do_check(struct verifier_env *env)
if (err)
return err;
dst_reg_type = regs[insn->dst_reg].type;
/* check that memory (dst_reg + off) is writeable */
err = check_mem_access(env, insn->dst_reg, insn->off,
BPF_SIZE(insn->code), BPF_WRITE,
@@ -1721,6 +1720,15 @@ static int do_check(struct verifier_env *env)
if (err)
return err;
if (insn->imm == 0) {
insn->imm = dst_reg_type;
} else if (dst_reg_type != insn->imm &&
(dst_reg_type == PTR_TO_CTX ||
insn->imm == PTR_TO_CTX)) {
verbose("same insn cannot be used with different pointers\n");
return -EINVAL;
}
} else if (class == BPF_ST) {
if (BPF_MODE(insn->code) != BPF_MEM ||
insn->src_reg != BPF_REG_0) {
@@ -1839,12 +1847,18 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env)
for (i = 0; i < insn_cnt; i++, insn++) {
if (BPF_CLASS(insn->code) == BPF_LDX &&
(BPF_MODE(insn->code) != BPF_MEM ||
insn->imm != 0)) {
(BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
verbose("BPF_LDX uses reserved fields\n");
return -EINVAL;
}
if (BPF_CLASS(insn->code) == BPF_STX &&
((BPF_MODE(insn->code) != BPF_MEM &&
BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
verbose("BPF_STX uses reserved fields\n");
return -EINVAL;
}
if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
struct bpf_map *map;
struct fd f;
@@ -1967,12 +1981,17 @@ static int convert_ctx_accesses(struct verifier_env *env)
struct bpf_prog *new_prog;
u32 cnt;
int i;
enum bpf_access_type type;
if (!env->prog->aux->ops->convert_ctx_access)
return 0;
for (i = 0; i < insn_cnt; i++, insn++) {
if (insn->code != (BPF_LDX | BPF_MEM | BPF_W))
if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
type = BPF_READ;
else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
type = BPF_WRITE;
else
continue;
if (insn->imm != PTR_TO_CTX) {
@@ -1982,7 +2001,7 @@ static int convert_ctx_accesses(struct verifier_env *env)
}
cnt = env->prog->aux->ops->
convert_ctx_access(insn->dst_reg, insn->src_reg,
convert_ctx_access(type, insn->dst_reg, insn->src_reg,
insn->off, insn_buf);
if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
verbose("bpf verifier is misconfigured\n");