netfilter: nf_tables: cancel tracking for clobbered destination registers

Output of expressions might be larger than one single register, this might
clobber existing data. Reset tracking for all destination registers that
required to store the expression output.

This patch adds three new helper functions:

- nft_reg_track_update: cancel previous register tracking and update it.
- nft_reg_track_cancel: cancel any previous register tracking info.
- __nft_reg_track_cancel: cancel only one single register tracking info.

Partial register clobbering detection is also supported by checking the
.num_reg field which describes the number of register that are used.

This patch updates the following expressions:

- meta_bridge
- bitwise
- byteorder
- meta
- payload

to use these helper functions.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -126,6 +126,7 @@ struct nft_regs_track {
 	struct {
 		const struct nft_expr		*selector;
 		const struct nft_expr		*bitwise;
+		u8				num_reg;
 	} regs[NFT_REG32_NUM];
 
 	const struct nft_expr			*cur;
@@ -1641,4 +1642,17 @@ static inline bool nft_reduce_is_readonly(const struct nft_expr *expr)
 	return expr->ops->reduce == NFT_REDUCE_READONLY;
 }
 
+void nft_reg_track_update(struct nft_regs_track *track,
+			  const struct nft_expr *expr, u8 dreg, u8 len);
+void nft_reg_track_cancel(struct nft_regs_track *track, u8 dreg, u8 len);
+void __nft_reg_track_cancel(struct nft_regs_track *track, u8 dreg);
+
+static inline bool nft_reg_track_cmp(struct nft_regs_track *track,
+				     const struct nft_expr *expr, u8 dreg)
+{
+	return track->regs[dreg].selector &&
+	       track->regs[dreg].selector->ops == expr->ops &&
+	       track->regs[dreg].num_reg == 0;
+}
+
 #endif /* _NET_NF_TABLES_H */

include/net/netfilter/nft_meta.h

@@ -6,6 +6,7 @@
 
 struct nft_meta {
 	enum nft_meta_keys	key:8;
+	u8			len;
 	union {
 		u8		dreg;
 		u8		sreg;

net/bridge/netfilter/nft_meta_bridge.c

@@ -87,6 +87,7 @@ static int nft_meta_bridge_get_init(const struct nft_ctx *ctx,
 		return nft_meta_get_init(ctx, expr, tb);
 	}
 
+	priv->len = len;
 	return nft_parse_register_store(ctx, tb[NFTA_META_DREG], &priv->dreg,
 					NULL, NFT_DATA_VALUE, len);
 }
@@ -112,8 +113,7 @@ static bool nft_meta_bridge_set_reduce(struct nft_regs_track *track,
 		if (track->regs[i].selector->ops != &nft_meta_bridge_get_ops)
 			continue;
 
-		track->regs[i].selector = NULL;
-		track->regs[i].bitwise = NULL;
+		__nft_reg_track_cancel(track, i);
 	}
 
 	return false;

net/netfilter/nf_tables_api.c

@@ -550,6 +550,58 @@ static int nft_delflowtable(struct nft_ctx *ctx,
 	return err;
 }
 
+static void __nft_reg_track_clobber(struct nft_regs_track *track, u8 dreg)
+{
+	int i;
+
+	for (i = track->regs[dreg].num_reg; i > 0; i--)
+		__nft_reg_track_cancel(track, dreg - i);
+}
+
+static void __nft_reg_track_update(struct nft_regs_track *track,
+				   const struct nft_expr *expr,
+				   u8 dreg, u8 num_reg)
+{
+	track->regs[dreg].selector = expr;
+	track->regs[dreg].bitwise = NULL;
+	track->regs[dreg].num_reg = num_reg;
+}
+
+void nft_reg_track_update(struct nft_regs_track *track,
+			  const struct nft_expr *expr, u8 dreg, u8 len)
+{
+	unsigned int regcount;
+	int i;
+
+	__nft_reg_track_clobber(track, dreg);
+
+	regcount = DIV_ROUND_UP(len, NFT_REG32_SIZE);
+	for (i = 0; i < regcount; i++, dreg++)
+		__nft_reg_track_update(track, expr, dreg, i);
+}
+EXPORT_SYMBOL_GPL(nft_reg_track_update);
+
+void nft_reg_track_cancel(struct nft_regs_track *track, u8 dreg, u8 len)
+{
+	unsigned int regcount;
+	int i;
+
+	__nft_reg_track_clobber(track, dreg);
+
+	regcount = DIV_ROUND_UP(len, NFT_REG32_SIZE);
+	for (i = 0; i < regcount; i++, dreg++)
+		__nft_reg_track_cancel(track, dreg);
+}
+EXPORT_SYMBOL_GPL(nft_reg_track_cancel);
+
+void __nft_reg_track_cancel(struct nft_regs_track *track, u8 dreg)
+{
+	track->regs[dreg].selector = NULL;
+	track->regs[dreg].bitwise = NULL;
+	track->regs[dreg].num_reg = 0;
+}
+EXPORT_SYMBOL_GPL(__nft_reg_track_cancel);
+
 /*
  * Tables
  */

net/netfilter/nft_bitwise.c

@@ -283,12 +283,16 @@ static bool nft_bitwise_reduce(struct nft_regs_track *track,
 {
 	const struct nft_bitwise *priv = nft_expr_priv(expr);
 	const struct nft_bitwise *bitwise;
+	unsigned int regcount;
+	u8 dreg;
+	int i;
 
 	if (!track->regs[priv->sreg].selector)
 		return false;
 
 	bitwise = nft_expr_priv(expr);
 	if (track->regs[priv->sreg].selector == track->regs[priv->dreg].selector &&
+	    track->regs[priv->sreg].num_reg == 0 &&
 	    track->regs[priv->dreg].bitwise &&
 	    track->regs[priv->dreg].bitwise->ops == expr->ops &&
 	    priv->sreg == bitwise->sreg &&
@@ -302,16 +306,20 @@ static bool nft_bitwise_reduce(struct nft_regs_track *track,
 		return true;
 	}
 
-	if (track->regs[priv->sreg].bitwise) {
-		track->regs[priv->dreg].selector = NULL;
-		track->regs[priv->dreg].bitwise = NULL;
+	if (track->regs[priv->sreg].bitwise ||
+	    track->regs[priv->sreg].num_reg != 0) {
+		nft_reg_track_cancel(track, priv->dreg, priv->len);
 		return false;
 	}
 
 	if (priv->sreg != priv->dreg) {
-		track->regs[priv->dreg].selector =
-			track->regs[priv->sreg].selector;
+		nft_reg_track_update(track, track->regs[priv->sreg].selector,
+				     priv->dreg, priv->len);
 	}
+
+	dreg = priv->dreg;
+	regcount = DIV_ROUND_UP(priv->len, NFT_REG32_SIZE);
+	for (i = 0; i < regcount; i++, dreg++)
 		track->regs[priv->dreg].bitwise = expr;
 
 	return false;
@@ -447,8 +455,7 @@ static bool nft_bitwise_fast_reduce(struct nft_regs_track *track,
 	}
 
 	if (track->regs[priv->sreg].bitwise) {
-		track->regs[priv->dreg].selector = NULL;
-		track->regs[priv->dreg].bitwise = NULL;
+		nft_reg_track_cancel(track, priv->dreg, NFT_REG32_SIZE);
 		return false;
 	}
 

net/netfilter/nft_byteorder.c

@@ -172,8 +172,7 @@ static bool nft_byteorder_reduce(struct nft_regs_track *track,
 {
 	struct nft_byteorder *priv = nft_expr_priv(expr);
 
-	track->regs[priv->dreg].selector = NULL;
-	track->regs[priv->dreg].bitwise = NULL;
+	nft_reg_track_cancel(track, priv->dreg, priv->len);
 
 	return false;
 }

net/netfilter/nft_meta.c

@@ -539,6 +539,7 @@ int nft_meta_get_init(const struct nft_ctx *ctx,
 		return -EOPNOTSUPP;
 	}
 
+	priv->len = len;
 	return nft_parse_register_store(ctx, tb[NFTA_META_DREG], &priv->dreg,
 					NULL, NFT_DATA_VALUE, len);
 }
@@ -664,6 +665,7 @@ int nft_meta_set_init(const struct nft_ctx *ctx,
 		return -EOPNOTSUPP;
 	}
 
+	priv->len = len;
 	err = nft_parse_register_load(tb[NFTA_META_SREG], &priv->sreg, len);
 	if (err < 0)
 		return err;
@@ -756,18 +758,15 @@ static bool nft_meta_get_reduce(struct nft_regs_track *track,
 	const struct nft_meta *priv = nft_expr_priv(expr);
 	const struct nft_meta *meta;
 
-	if (!track->regs[priv->dreg].selector ||
-	    track->regs[priv->dreg].selector->ops != expr->ops) {
-		track->regs[priv->dreg].selector = expr;
-		track->regs[priv->dreg].bitwise = NULL;
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
 		return false;
 	}
 
 	meta = nft_expr_priv(track->regs[priv->dreg].selector);
 	if (priv->key != meta->key ||
 	    priv->dreg != meta->dreg) {
-		track->regs[priv->dreg].selector = expr;
-		track->regs[priv->dreg].bitwise = NULL;
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
 		return false;
 	}
 
@@ -800,8 +799,7 @@ static bool nft_meta_set_reduce(struct nft_regs_track *track,
 		if (track->regs[i].selector->ops != &nft_meta_get_ops)
 			continue;
 
-		track->regs[i].selector = NULL;
-		track->regs[i].bitwise = NULL;
+		__nft_reg_track_cancel(track, i);
 	}
 
 	return false;

net/netfilter/nft_payload.c

@@ -216,10 +216,8 @@ static bool nft_payload_reduce(struct nft_regs_track *track,
 	const struct nft_payload *priv = nft_expr_priv(expr);
 	const struct nft_payload *payload;
 
-	if (!track->regs[priv->dreg].selector ||
-	    track->regs[priv->dreg].selector->ops != expr->ops) {
-		track->regs[priv->dreg].selector = expr;
-		track->regs[priv->dreg].bitwise = NULL;
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
 		return false;
 	}
 
@@ -227,8 +225,7 @@ static bool nft_payload_reduce(struct nft_regs_track *track,
 	if (priv->base != payload->base ||
 	    priv->offset != payload->offset ||
 	    priv->len != payload->len) {
-		track->regs[priv->dreg].selector = expr;
-		track->regs[priv->dreg].bitwise = NULL;
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
 		return false;
 	}
 
@@ -815,8 +812,7 @@ static bool nft_payload_set_reduce(struct nft_regs_track *track,
 		    track->regs[i].selector->ops != &nft_payload_fast_ops)
 			continue;
 
-		track->regs[i].selector = NULL;
-		track->regs[i].bitwise = NULL;
+		__nft_reg_track_cancel(track, i);
 	}
 
 	return false;