bpf: add generic bpf_csum_diff helper
For L4 checksums, we currently have bpf_l4_csum_replace() helper. It's
currently limited to handle 2 and 4 byte changes in a header and feeds the
from/to into inet_proto_csum_replace{2,4}() helpers of the kernel. When
working with IPv6, for example, this makes it rather cumbersome to deal
with, similarly when editing larger parts of a header.
Instead, extend the API in a more generic way: For bpf_l4_csum_replace(),
add a case for header field mask of 0 to change the checksum at a given
offset through inet_proto_csum_replace_by_diff(), and provide a helper
bpf_csum_diff() that can generically calculate a from/to diff for arbitrary
amounts of data.
This can be used in multiple ways: for the bpf_l4_csum_replace() only
part, this even provides us with the option to insert precalculated diffs
from user space f.e. from a map, or from bpf_csum_diff() during runtime.
bpf_csum_diff() has a optional from/to stack buffer input, so we can
calculate a diff by using a scratchbuffer for scenarios where we're
inserting (from is NULL), removing (to is NULL) or diffing (from/to buffers
don't need to be of equal size) data. Also, bpf_csum_diff() allows to
feed a previous csum into csum_partial(), so the function can also be
cascaded.
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/net/core/filter.c b/net/core/filter.c
index 2a6e956..bf504f8 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1491,6 +1491,12 @@
return -EFAULT;
switch (flags & BPF_F_HDR_FIELD_MASK) {
+ case 0:
+ if (unlikely(from != 0))
+ return -EINVAL;
+
+ inet_proto_csum_replace_by_diff(ptr, skb, to, is_pseudo);
+ break;
case 2:
inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo);
break;
@@ -1519,6 +1525,51 @@
.arg5_type = ARG_ANYTHING,
};
+struct bpf_csum_scratchpad {
+ __be32 diff[128];
+};
+
+static DEFINE_PER_CPU(struct bpf_csum_scratchpad, bpf_csum_sp);
+
+static u64 bpf_csum_diff(u64 r1, u64 from_size, u64 r3, u64 to_size, u64 seed)
+{
+ struct bpf_csum_scratchpad *sp = this_cpu_ptr(&bpf_csum_sp);
+ u64 diff_size = from_size + to_size;
+ __be32 *from = (__be32 *) (long) r1;
+ __be32 *to = (__be32 *) (long) r3;
+ int i, j = 0;
+
+ /* This is quite flexible, some examples:
+ *
+ * from_size == 0, to_size > 0, seed := csum --> pushing data
+ * from_size > 0, to_size == 0, seed := csum --> pulling data
+ * from_size > 0, to_size > 0, seed := 0 --> diffing data
+ *
+ * Even for diffing, from_size and to_size don't need to be equal.
+ */
+ if (unlikely(((from_size | to_size) & (sizeof(__be32) - 1)) ||
+ diff_size > sizeof(sp->diff)))
+ return -EINVAL;
+
+ for (i = 0; i < from_size / sizeof(__be32); i++, j++)
+ sp->diff[j] = ~from[i];
+ for (i = 0; i < to_size / sizeof(__be32); i++, j++)
+ sp->diff[j] = to[i];
+
+ return csum_partial(sp->diff, diff_size, seed);
+}
+
+const struct bpf_func_proto bpf_csum_diff_proto = {
+ .func = bpf_csum_diff,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_STACK,
+ .arg2_type = ARG_CONST_STACK_SIZE_OR_ZERO,
+ .arg3_type = ARG_PTR_TO_STACK,
+ .arg4_type = ARG_CONST_STACK_SIZE_OR_ZERO,
+ .arg5_type = ARG_ANYTHING,
+};
+
static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
{
struct sk_buff *skb = (struct sk_buff *) (long) r1, *skb2;
@@ -1849,6 +1900,8 @@
return &bpf_skb_store_bytes_proto;
case BPF_FUNC_skb_load_bytes:
return &bpf_skb_load_bytes_proto;
+ case BPF_FUNC_csum_diff:
+ return &bpf_csum_diff_proto;
case BPF_FUNC_l3_csum_replace:
return &bpf_l3_csum_replace_proto;
case BPF_FUNC_l4_csum_replace: