From: John Fastabend <john.fastab...@gmail.com>
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.fastab...@gmail.com>
Acked-by: Daniel Borkmann <dan...@iogearbox.net>
---
net/core/filter.c | 2 +-
tools/testing/selftests/bpf/test_verifier.c | 16 ++++++++++++++--
2 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index ca1ba0b..aa02659 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -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):
diff --git a/tools/testing/selftests/bpf/test_verifier.c
b/tools/testing/selftests/bpf/test_verifier.c
index 26f3250..16cca57 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -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",
