proto: track full stack of seen l2 protocols, not just cumulative offset

For input, a cumulative size counter of all pushed l2 headers is enough,
because we have the full expression tree available to us.

For delinearization we need to track all seen l2 headers, else we lose
information that we might need at a later time.

Consider:

rule netdev nt nc set update ether saddr . vlan id

during delinearization, the vlan proto_desc replaces the ethernet one,
and by the time we try to split the concatenation apart we will search
the ether saddr offset vs. the templates for proto_vlan.

This replaces the offset with an array that stores the protocol
descriptions seen.

Then, if the payload offset is larger than our description, search the
l2 stack and adjust the offset until we're within the expected offset
boundary.

Reported-by: Eric Garver <eric@garver.life>
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 56 insertions, 11 deletions

diff --git a/src/payload.c b/src/payload.c
index 66418cdd..2c0d0ac9 100644
--- a/src/payload.c
+++ b/src/payload.c
@@ -116,8 +116,13 @@ static void payload_expr_pctx_update(struct proto_ctx *ctx,
 	if (desc->base == base->base) {
 		assert(base->length > 0);
 
-		if (!left->payload.is_raw)
-			ctx->protocol[base->base].offset += base->length;
+		if (!left->payload.is_raw) {
+			if (desc->base == PROTO_BASE_LL_HDR &&
+			    ctx->stacked_ll_count < PROTO_CTX_NUM_PROTOS) {
+				ctx->stacked_ll[ctx->stacked_ll_count] = base;
+				ctx->stacked_ll_count++;
+			}
+		}
 	}
 	proto_ctx_update(ctx, desc->base, loc, desc);
 }
@@ -869,6 +874,38 @@ void exthdr_dependency_kill(struct payload_dep_ctx *ctx, struct expr *expr,
 	}
 }
 
+static const struct proto_desc *get_stacked_desc(const struct proto_ctx *ctx,
+						 const struct proto_desc *top,
+						 const struct expr *e,
+						 unsigned int *skip)
+{
+	unsigned int i, total, payload_offset = e->payload.offset;
+
+	assert(e->etype == EXPR_PAYLOAD);
+
+	if (e->payload.base != PROTO_BASE_LL_HDR ||
+	    payload_offset < top->length) {
+		*skip = 0;
+		return top;
+	}
+
+	for (i = 0, total = 0; i < ctx->stacked_ll_count; i++) {
+		const struct proto_desc *stacked;
+
+		stacked = ctx->stacked_ll[i];
+		if (payload_offset < stacked->length) {
+			*skip = total;
+			return stacked;
+		}
+
+		payload_offset -= stacked->length;
+		total += stacked->length;
+	}
+
+	*skip = total;
+	return top;
+}
+
 /**
  * payload_expr_complete - fill in type information of a raw payload expr
  *
@@ -880,9 +917,10 @@ void exthdr_dependency_kill(struct payload_dep_ctx *ctx, struct expr *expr,
  */
 void payload_expr_complete(struct expr *expr, const struct proto_ctx *ctx)
 {
+	unsigned int payload_offset = expr->payload.offset;
 	const struct proto_desc *desc;
 	const struct proto_hdr_template *tmpl;
-	unsigned int i;
+	unsigned int i, total;
 
 	assert(expr->etype == EXPR_PAYLOAD);
 
@@ -891,9 +929,12 @@ void payload_expr_complete(struct expr *expr, const struct proto_ctx *ctx)
 		return;
 	assert(desc->base == expr->payload.base);
 
+	desc = get_stacked_desc(ctx, desc, expr, &total);
+	payload_offset -= total;
+
 	for (i = 0; i < array_size(desc->templates); i++) {
 		tmpl = &desc->templates[i];
-		if (tmpl->offset != expr->payload.offset ||
+		if (tmpl->offset != payload_offset ||
 		    tmpl->len    != expr->len)
 			continue;
 
@@ -950,6 +991,7 @@ bool payload_expr_trim(struct expr *expr, struct expr *mask,
 	unsigned int payload_len = expr->len;
 	const struct proto_desc *desc;
 	unsigned int off, i, len = 0;
+	unsigned int total;
 
 	assert(expr->etype == EXPR_PAYLOAD);
 
@@ -959,10 +1001,8 @@ bool payload_expr_trim(struct expr *expr, struct expr *mask,
 
 	assert(desc->base == expr->payload.base);
 
-	if (ctx->protocol[expr->payload.base].offset) {
-		assert(payload_offset >= ctx->protocol[expr->payload.base].offset);
-		payload_offset -= ctx->protocol[expr->payload.base].offset;
-	}
+	desc = get_stacked_desc(ctx, desc, expr, &total);
+	payload_offset -= total;
 
 	off = round_up(mask->len, BITS_PER_BYTE) - mask_len;
 	payload_offset += off;
@@ -1009,10 +1049,11 @@ bool payload_expr_trim(struct expr *expr, struct expr *mask,
 void payload_expr_expand(struct list_head *list, struct expr *expr,
 			 const struct proto_ctx *ctx)
 {
+	unsigned int payload_offset = expr->payload.offset;
 	const struct proto_hdr_template *tmpl;
 	const struct proto_desc *desc;
+	unsigned int i, total;
 	struct expr *new;
-	unsigned int i;
 
 	assert(expr->etype == EXPR_PAYLOAD);
 
@@ -1021,13 +1062,16 @@ void payload_expr_expand(struct list_head *list, struct expr *expr,
 		goto raw;
 	assert(desc->base == expr->payload.base);
 
+	desc = get_stacked_desc(ctx, desc, expr, &total);
+	payload_offset -= total;
+
 	for (i = 1; i < array_size(desc->templates); i++) {
 		tmpl = &desc->templates[i];
 
 		if (tmpl->len == 0)
 			break;
 
-		if (tmpl->offset != expr->payload.offset)
+		if (tmpl->offset != payload_offset)
 			continue;
 
 		if (tmpl->icmp_dep && ctx->th_dep.icmp.type &&
@@ -1039,6 +1083,7 @@ void payload_expr_expand(struct list_head *list, struct expr *expr,
 			list_add_tail(&new->list, list);
 			expr->len	     -= tmpl->len;
 			expr->payload.offset += tmpl->len;
+			payload_offset       += tmpl->len;
 			if (expr->len == 0)
 				return;
 		} else if (expr->len > 0) {
@@ -1051,7 +1096,7 @@ void payload_expr_expand(struct list_head *list, struct expr *expr,
 	}
 raw:
 	new = payload_expr_alloc(&expr->location, NULL, 0);
-	payload_init_raw(new, expr->payload.base, expr->payload.offset,
+	payload_init_raw(new, expr->payload.base, payload_offset,
 			 expr->len);
 	list_add_tail(&new->list, list);
 }