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>

1 files changed, 4 insertions, 8 deletions

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index 5cc06aef43452a..2e7ac007cb30fe 100644
--- a/net/netfilter/nft_payload.c
+++ b/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;