When programs need to calculate the csum from scratch for small UDP
packets and use bpf_l4_csum_replace() to feed the result from helpers
like bpf_csum_diff(), then we need a flag besides BPF_F_MARK_MANGLED_0
that would ignore the case of current csum being 0, and which would
still allow for the helper to set the csum and transform when needed
to CSUM_MANGLED_0.
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Acked-by: Alexei Starovoitov <a...@kernel.org>
---
include/uapi/linux/bpf.h | 1 +
net/core/filter.c | 7 ++++---
2 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index bd30684..e07fd5a 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -522,6 +522,7 @@ enum bpf_func_id {
/* BPF_FUNC_l4_csum_replace flags. */
#define BPF_F_PSEUDO_HDR (1ULL << 4)
#define BPF_F_MARK_MANGLED_0 (1ULL << 5)
+#define BPF_F_MARK_ENFORCE (1ULL << 6)
/* BPF_FUNC_clone_redirect and BPF_FUNC_redirect flags. */
#define BPF_F_INGRESS (1ULL << 0)
diff --git a/net/core/filter.c b/net/core/filter.c
index e2263da..1e00737 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1522,10 +1522,11 @@ static inline void bpf_pull_mac_rcsum(struct sk_buff
*skb)
{
bool is_pseudo = flags & BPF_F_PSEUDO_HDR;
bool is_mmzero = flags & BPF_F_MARK_MANGLED_0;
+ bool do_mforce = flags & BPF_F_MARK_ENFORCE;
__sum16 *ptr;
- if (unlikely(flags & ~(BPF_F_MARK_MANGLED_0 | BPF_F_PSEUDO_HDR |
- BPF_F_HDR_FIELD_MASK)))
+ if (unlikely(flags & ~(BPF_F_MARK_MANGLED_0 | BPF_F_MARK_ENFORCE |
+ BPF_F_PSEUDO_HDR | BPF_F_HDR_FIELD_MASK)))
return -EINVAL;
if (unlikely(offset > 0xffff || offset & 1))
return -EFAULT;
@@ -1533,7 +1534,7 @@ static inline void bpf_pull_mac_rcsum(struct sk_buff *skb)
return -EFAULT;
ptr = (__sum16 *)(skb->data + offset);
- if (is_mmzero && !*ptr)
+ if (is_mmzero && !do_mforce && !*ptr)
return 0;
switch (flags & BPF_F_HDR_FIELD_MASK) {
--
1.9.3
