[PATCH nft 7/9] expression: cleanup expr_ops_by_type() and handle u32 input

[Thomas Haller <thaller@xxxxxxxxxx>]

Be more careful about casting an uint32_t value to "enum expr_types" and
make fewer assumptions about the underlying integer type of the enum.
Instead, be clear about where we have an untrusted uint32_t from netlink
and an enum. Rename expr_ops_by_type() to expr_ops_by_type_u32() to make
this clearer. Later we might make the enum as packed, when this starts
to matter more.

Also, only the code path expr_ops() wants strict validation and assert
against valid enum values. Move the assertion out of
__expr_ops_by_type(). Then expr_ops_by_type_u32() does not need to
duplicate the handling of EXPR_INVALID. We still need to duplicate the
check against EXPR_MAX, to ensure that the uint32_t value can be cast to
an enum value.

Signed-off-by: Thomas Haller <thaller@xxxxxxxxxx>
---
 include/expression.h |  2 +-
 src/expression.c     | 23 +++++++++++------------
 src/netlink.c        |  4 ++--
 3 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/include/expression.h b/include/expression.h
index 469f41ecd613..aede223db741 100644
--- a/include/expression.h
+++ b/include/expression.h
@@ -189,7 +189,7 @@ struct expr_ops {
 };
 
 const struct expr_ops *expr_ops(const struct expr *e);
-const struct expr_ops *expr_ops_by_type(enum expr_types etype);
+const struct expr_ops *expr_ops_by_type_u32(uint32_t value);
 
 /**
  * enum expr_flags
diff --git a/src/expression.c b/src/expression.c
index 87d5a9fcbe09..320c02be522c 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -995,7 +995,7 @@ static struct expr *concat_expr_parse_udata(const struct nftnl_udata *attr)
 			goto err_free;
 
 		etype = nftnl_udata_get_u32(nest_ud[NFTNL_UDATA_SET_KEY_CONCAT_SUB_TYPE]);
-		ops = expr_ops_by_type(etype);
+		ops = expr_ops_by_type_u32(etype);
 		if (!ops || !ops->parse_udata)
 			goto err_free;
 
@@ -1509,9 +1509,7 @@ void range_expr_value_high(mpz_t rop, const struct expr *expr)
 static const struct expr_ops *__expr_ops_by_type(enum expr_types etype)
 {
 	switch (etype) {
-	case EXPR_INVALID:
-		BUG("Invalid expression ops requested");
-		break;
+	case EXPR_INVALID: break;
 	case EXPR_VERDICT: return &verdict_expr_ops;
 	case EXPR_SYMBOL: return &symbol_expr_ops;
 	case EXPR_VARIABLE: return &variable_expr_ops;
@@ -1543,21 +1541,22 @@ static const struct expr_ops *__expr_ops_by_type(enum expr_types etype)
 	case EXPR_FLAGCMP: return &flagcmp_expr_ops;
 	}
 
-	BUG("Unknown expression type %d\n", etype);
+	return NULL;
 }
 
 const struct expr_ops *expr_ops(const struct expr *e)
 {
-	return __expr_ops_by_type(e->etype);
+	const struct expr_ops *ops;
+
+	ops = __expr_ops_by_type(e->etype);
+	if (!ops)
+		BUG("Unknown expression type %d\n", e->etype);
+	return ops;
 }
 
-const struct expr_ops *expr_ops_by_type(enum expr_types value)
+const struct expr_ops *expr_ops_by_type_u32(uint32_t value)
 {
-	/* value might come from unreliable source, such as "udata"
-	 * annotation of set keys.  Avoid BUG() assertion.
-	 */
-	if (value == EXPR_INVALID || value > EXPR_MAX)
+	if (value > (uint32_t) EXPR_MAX)
 		return NULL;
-
 	return __expr_ops_by_type(value);
 }
diff --git a/src/netlink.c b/src/netlink.c
index 70ebf382b14f..8af579c7b778 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -878,8 +878,8 @@ static struct expr *set_make_key(const struct nftnl_udata *attr)
 {
 	const struct nftnl_udata *ud[NFTNL_UDATA_SET_TYPEOF_MAX + 1] = {};
 	const struct expr_ops *ops;
-	enum expr_types etype;
 	struct expr *expr;
+	uint32_t etype;
 	int err;
 
 	if (!attr)
@@ -895,7 +895,7 @@ static struct expr *set_make_key(const struct nftnl_udata *attr)
 		return NULL;
 
 	etype = nftnl_udata_get_u32(ud[NFTNL_UDATA_SET_TYPEOF_EXPR]);
-	ops = expr_ops_by_type(etype);
+	ops = expr_ops_by_type_u32(etype);
 	if (!ops)
 		return NULL;
 
-- 
2.41.0