src: evaluate: reset context maxlen value before prio evaluation

unshare -n tests/shell/run-tests.sh tests/shell/testcases/nft-f/0024priority_0
W: [FAILED]     tests/shell/testcases/nft-f/0024priority_0: got 1
/dev/stdin:8:47-49: Error: Value 100 exceeds valid range 0-15
        type filter hook postrouting priority 100

Reported-by: Andreas Schultz <andreas.schultz@travelping.com
Signed-off-by: Florian Westphal <fw@strlen.de>

3 files changed, 26 insertions, 2 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 7d6f55fe..3a91e9ea 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -3789,8 +3789,8 @@ static bool evaluate_priority(struct eval_ctx *ctx, struct prio_spec *prio,
 	int prio_snd;
 	char op;
 
-	ctx->ectx.dtype = &priority_type;
-	ctx->ectx.len = NFT_NAME_MAXLEN * BITS_PER_BYTE;
+	expr_set_context(&ctx->ectx, &priority_type, NFT_NAME_MAXLEN * BITS_PER_BYTE);
+
 	if (expr_evaluate(ctx, &prio->expr) < 0)
 		return false;
 	if (prio->expr->etype != EXPR_VALUE) {
diff --git a/tests/shell/testcases/nft-f/0024priority_0 b/tests/shell/testcases/nft-f/0024priority_0
new file mode 100755
index 00000000..586f5c3f
--- /dev/null
+++ b/tests/shell/testcases/nft-f/0024priority_0
@@ -0,0 +1,14 @@
+#!/bin/bash
+
+RULESET="
+table inet statelessnat {
+    chain prerouting {
+        type filter hook prerouting priority -100;
+        ip daddr set numgen inc mod 16 map { 0-7 : 10.0.1.1, 8- 15 : 10.0.1.2 }
+    }
+    chain postrouting {
+        type filter hook postrouting priority 100
+    }
+}"
+
+exec $NFT -f - <<< "$RULESET"
diff --git a/tests/shell/testcases/nft-f/dumps/0024priority_0.nft b/tests/shell/testcases/nft-f/dumps/0024priority_0.nft
new file mode 100644
index 00000000..cd7fc504
--- /dev/null
+++ b/tests/shell/testcases/nft-f/dumps/0024priority_0.nft
@@ -0,0 +1,10 @@
+table inet statelessnat {
+	chain prerouting {
+		type filter hook prerouting priority dstnat; policy accept;
+		ip daddr set numgen inc mod 16 map { 0-7 : 10.0.1.1, 8-15 : 10.0.1.2 }
+	}
+
+	chain postrouting {
+		type filter hook postrouting priority srcnat; policy accept;
+	}
+}