[PATCH nft] evaluate: error out when store needs more than one 128bit register of align fixup

[Florian Westphal <fw@strlen.de>]

Else this gives:
nft: evaluate.c:2983: stmt_evaluate_payload: Assertion `sizeof(data) * BITS_PER_BYTE >= masklen' failed.

For loads, this is already prevented via expr_evaluate_bits() which has:

  if (masklen > NFT_REG_SIZE * BITS_PER_BYTE)
      return expr_error(ctx->msgs, expr, "mask length %u exceeds allowed maximum of %u\n",
                        masklen, NFT_REG_SIZE * BITS_PER_BYTE);

But for the store path this isn't called.
The reproducer asks to store a 128 bit integer at bit offset 1, i.e.
17 bytes would need to be munged, but we can only handle up to 16 bytes
(one pseudo-register).

Fixes: 78936d50f306 ("evaluate: add support to set IPv6 non-byte header fields")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/evaluate.c                                               | 5 +++++
 .../testcases/bogons/nft-f/payload_expr_unaligned_store      | 1 +
 2 files changed, 6 insertions(+)
 create mode 100644 tests/shell/testcases/bogons/nft-f/payload_expr_unaligned_store

diff --git a/src/evaluate.c b/src/evaluate.c
index 5576b56ece67..1adec037b04b 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -3188,6 +3188,11 @@ static int stmt_evaluate_payload(struct eval_ctx *ctx, struct stmt *stmt)
 	payload_byte_size = div_round_up(payload->len + extra_len,
 					 BITS_PER_BYTE);
 
+	if (payload_byte_size > sizeof(data))
+		return expr_error(ctx->msgs, stmt->payload.expr,
+				  "uneven load cannot span more than %u bytes, got %u",
+				  sizeof(data), payload_byte_size);
+
 	if (need_csum && payload_byte_size & 1) {
 		payload_byte_size++;
 
diff --git a/tests/shell/testcases/bogons/nft-f/payload_expr_unaligned_store b/tests/shell/testcases/bogons/nft-f/payload_expr_unaligned_store
new file mode 100644
index 000000000000..c1358df45e93
--- /dev/null
+++ b/tests/shell/testcases/bogons/nft-f/payload_expr_unaligned_store
@@ -0,0 +1 @@
+add rule f i @th,1,128 set 1
-- 
2.43.0