bpf: fix csum update in bpf_l4_csum_replace helper for udp
When using this helper for updating UDP checksums, we need to extend
this in order to write CSUM_MANGLED_0 for csum computations that result
into 0 as sum. Reason we need this is because packets with a checksum
could otherwise become incorrectly marked as a packet without a checksum.
Likewise, if the user indicates BPF_F_MARK_MANGLED_0, then we should
not turn packets without a checksum into ones with a checksum.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 48d0a6c..6496f98 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -313,6 +313,7 @@
/* BPF_FUNC_l4_csum_replace flags. */
#define BPF_F_PSEUDO_HDR (1ULL << 4)
+#define BPF_F_MARK_MANGLED_0 (1ULL << 5)
/* 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 f031b82..8a0b8c3 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1477,10 +1477,12 @@
{
struct sk_buff *skb = (struct sk_buff *) (long) r1;
bool is_pseudo = flags & BPF_F_PSEUDO_HDR;
+ bool is_mmzero = flags & BPF_F_MARK_MANGLED_0;
int offset = (int) r2;
__sum16 sum, *ptr;
- if (unlikely(flags & ~(BPF_F_PSEUDO_HDR | BPF_F_HDR_FIELD_MASK)))
+ if (unlikely(flags & ~(BPF_F_MARK_MANGLED_0 | BPF_F_PSEUDO_HDR |
+ BPF_F_HDR_FIELD_MASK)))
return -EINVAL;
if (unlikely((u32) offset > 0xffff))
return -EFAULT;
@@ -1490,6 +1492,8 @@
ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);
if (unlikely(!ptr))
return -EFAULT;
+ if (is_mmzero && !*ptr)
+ return 0;
switch (flags & BPF_F_HDR_FIELD_MASK) {
case 0:
@@ -1508,6 +1512,8 @@
return -EINVAL;
}
+ if (is_mmzero && !*ptr)
+ *ptr = CSUM_MANGLED_0;
if (ptr == &sum)
/* skb_store_bits guaranteed to not return -EFAULT here */
skb_store_bits(skb, offset, ptr, sizeof(sum));