[PATCH nft] evaluate: prevent assert when evaluating very large shift values

[Florian Westphal <fw@strlen.de>]

Error out instead of 'nft: gmputil.c:67: mpz_get_uint32: Assertion `cnt <= 1' failed.'.

Fixes: edecd58755a8 ("evaluate: support shifts larger than the width of the left operand")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/evaluate.c                                       | 9 +++++++--
 tests/shell/testcases/bogons/nft-f/huge_shift_assert | 5 +++++
 2 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 tests/shell/testcases/bogons/nft-f/huge_shift_assert

diff --git a/src/evaluate.c b/src/evaluate.c
index 048880e54daf..e4dc5f65e3bd 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -1312,9 +1312,14 @@ static int constant_binop_simplify(struct eval_ctx *ctx, struct expr **expr)
 static int expr_evaluate_shift(struct eval_ctx *ctx, struct expr **expr)
 {
 	struct expr *op = *expr, *left = op->left, *right = op->right;
-	unsigned int shift = mpz_get_uint32(right->value);
-	unsigned int max_shift_len;
+	unsigned int shift, max_shift_len;
 
+	/* mpz_get_uint32 has assert() for huge values */
+	if (mpz_cmp_ui(right->value, UINT_MAX) > 0)
+		return expr_binary_error(ctx->msgs, right, left,
+					 "shifts exceeding %u bits are not supported", UINT_MAX);
+
+	shift = mpz_get_uint32(right->value);
 	if (ctx->stmt_len > left->len)
 		max_shift_len = ctx->stmt_len;
 	else
diff --git a/tests/shell/testcases/bogons/nft-f/huge_shift_assert b/tests/shell/testcases/bogons/nft-f/huge_shift_assert
new file mode 100644
index 000000000000..7599f8505209
--- /dev/null
+++ b/tests/shell/testcases/bogons/nft-f/huge_shift_assert
@@ -0,0 +1,5 @@
+table ip t {
+        chain c {
+		counter name meta mark >> 88888888888888888888
+        }
+}
-- 
2.41.0