fib: Fix for existence check on Big Endian

Adjust the expression size to 1B so cmp expression value is correct.
Without this, the rule 'fib saddr . iif check exists' generates
following byte code on BE:

|  [ fib saddr . iif oif present => reg 1 ]
|  [ cmp eq reg 1 0x00000001 ]

Though with NFTA_FIB_F_PRESENT flag set, nft_fib.ko writes to the first
byte of reg 1 only (using nft_reg_store8()). With this patch in place,
byte code is correct:

|  [ fib saddr . iif oif present => reg 1 ]
|  [ cmp eq reg 1 0x01000000 ]

Fixes: f686a17eafa0b ("fib: Support existence check")
Cc: Yi Chen <yiche@redhat.com>
Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 4 insertions, 1 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 8cecbe09..6a1aa496 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -3002,6 +3002,7 @@ static int expr_evaluate_fib(struct eval_ctx *ctx, struct expr **exprp)
 	if (expr->flags & EXPR_F_BOOLEAN) {
 		expr->fib.flags |= NFTA_FIB_F_PRESENT;
 		datatype_set(expr, &boolean_type);
+		expr->len = BITS_PER_BYTE;
 	}
 	return expr_evaluate_primary(ctx, exprp);
 }
diff --git a/src/fib.c b/src/fib.c
index 53836132..4db7cd2b 100644
--- a/src/fib.c
+++ b/src/fib.c
@@ -198,8 +198,10 @@ struct expr *fib_expr_alloc(const struct location *loc,
 		BUG("Unknown result %d\n", result);
 	}
 
-	if (flags & NFTA_FIB_F_PRESENT)
+	if (flags & NFTA_FIB_F_PRESENT) {
 		type = &boolean_type;
+		len = BITS_PER_BYTE;
+	}
 
 	expr = expr_alloc(loc, EXPR_FIB, type,
 			  BYTEORDER_HOST_ENDIAN, len);