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bpf: remove mark access for SK_SKB program types

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The skb->mark field is a union with reserved_tailroom which is used
in the TCP code paths from stream memory allocation. Allowing SK_SKB
programs to set this field creates a conflict with future code
optimizations, such as "gifting" the skb to the egress path instead
of creating a new skb and doing a memcpy.

Because we do not have a released version of SK_SKB yet lets just
remove it for now. A more appropriate scratch pad to use at the
socket layer is dev_scratch, but lets add that in future kernels
when needed.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
John Fastabend 2017-10-18 07:10:58 -07:00 committed by David S. Miller
parent 34f79502bb
commit f7e9cb1ecb
2 changed files with 15 additions and 3 deletions
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2
net/core/filter.c
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@ -3684,7 +3684,6 @@ static bool sk_skb_is_valid_access(int off, int size,
{
if (type == BPF_WRITE) {
switch (off) {
case bpf_ctx_range(struct __sk_buff, mark):
case bpf_ctx_range(struct __sk_buff, tc_index):
case bpf_ctx_range(struct __sk_buff, priority):
break;
@ -3694,6 +3693,7 @@ static bool sk_skb_is_valid_access(int off, int size,
}
switch (off) {
case bpf_ctx_range(struct __sk_buff, mark):
case bpf_ctx_range(struct __sk_buff, tc_classid):
return false;
case bpf_ctx_range(struct __sk_buff, data):

16
tools/testing/selftests/bpf/test_verifier.c
View File

@ -1130,15 +1130,27 @@ static struct bpf_test tests[] = {
.errstr = "invalid bpf_context access",
},
{
"check skb->mark is writeable by SK_SKB",
"invalid access of skb->mark for SK_SKB",
.insns = {
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, mark)),
BPF_EXIT_INSN(),
},
.result = REJECT,
.prog_type = BPF_PROG_TYPE_SK_SKB,
.errstr = "invalid bpf_context access",
},
{
"check skb->mark is not writeable by SK_SKB",
.insns = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
offsetof(struct __sk_buff, mark)),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
.result = REJECT,
.prog_type = BPF_PROG_TYPE_SK_SKB,
.errstr = "invalid bpf_context access",
},
{
"check skb->tc_index is writeable by SK_SKB",