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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
2015-06-04 10:11:54 -07:00
committed by David S. Miller
parent 3431205e03
commit d691f9e8d4
6 changed files with 207 additions and 48 deletions
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84
samples/bpf/test_verifier.c
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@@ -29,6 +29,7 @@ struct bpf_test {
ACCEPT,
REJECT
} result;
enum bpf_prog_type prog_type;
};
static struct bpf_test tests[] = {
@@ -743,6 +744,84 @@ static struct bpf_test tests[] = {
.errstr = "different pointers",
.result = REJECT,
},
{
"check skb->mark is not writeable by sockets",
.insns = {
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, mark)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check skb->tc_index is not writeable by sockets",
.insns = {
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, tc_index)),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"check non-u32 access to cb",
.insns = {
BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_1,
offsetof(struct __sk_buff, cb[0])),
BPF_EXIT_INSN(),
},
.errstr = "invalid bpf_context access",
.result = REJECT,
},
{
"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) {