Enforce comment on structure layout dependency with a BUILD_BUG_ON
to ensure the condition is maintained.
Suggested-by: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: John Fastabend <john.fastab...@gmail.com>
---
include/linux/skmsg.h | 4 +---
net/core/filter.c | 3 +++
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index eb8f6cb..dd57e6f4 100644
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -36,9 +36,7 @@ struct sk_msg_sg {
struct scatterlist data[MAX_MSG_FRAGS + 1];
};
-/* UAPI in filter.c depends on struct sk_msg_sg being first element. If
- * this is moved filter.c also must be updated.
- */
+/* UAPI in filter.c depends on struct sk_msg_sg being first element. */
struct sk_msg {
struct sk_msg_sg sg;
void *data;
diff --git a/net/core/filter.c b/net/core/filter.c
index 6bd9f08..447dd1b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7425,6 +7425,9 @@ static u32 sk_msg_convert_ctx_access(enum bpf_access_type
type,
int off;
#endif
+ /* convert ctx uses the fact sg element is first in struct */
+ BUILD_BUG_ON(offsetof(struct sk_msg, sg) != 0);
+
switch (si->off) {
case offsetof(struct sk_msg_md, data):
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_msg, data),
--
2.7.4
