evaluate: fix segfault when adding elements to invalid set

Adding elements to a set or map with an invalid definition causes nft to
segfault. The following nftables.conf triggers the crash:

    flush ruleset
    create table inet filter
    set inet filter foo {}
    add element inet filter foo { foobar }

Simply parsing and checking the config will trigger it:

    $ nft -c -f nftables.conf.crash
    Segmentation fault

The error in the set/map definition is correctly caught and queued, but
because the set is invalid and does not contain a key type, adding to it
causes a NULL pointer dereference of set->key within setelem_evaluate().

I don't think it's necessary to queue another error since the underlying
problem is correctly detected and reported when parsing the definition
of the set. Simply checking the validity of set->key before using it
seems to fix it, causing the error in the definition of the set to be
reported properly. The element type error isn't caught, but that seems
reasonable since the key type is invalid or unknown anyway:

    $ ./nft -c -f ~/nftables.conf.crash
    /home/pti/nftables.conf.crash:3:21-21: Error: set definition does not specify key
    set inet filter foo {}
                        ^

[ Add tests to cover this case --pablo ]

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1597
Signed-off-by: Peter Tirsek <peter@tirsek.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/shell/testcases/sets/errors_0 b/tests/shell/testcases/sets/errors_0
index a676ac73..569f4ab8 100755
--- a/tests/shell/testcases/sets/errors_0
+++ b/tests/shell/testcases/sets/errors_0
@@ -27,4 +27,15 @@ delete element x y { 1.1.1.1/24 }
 add element x y { 1.1.1.1/24 }
 delete element x y { 2.2.2.2/24 }"
 
+$NFT -f - <<< $RULESET
+if [ $? -eq 0 ]
+then
+	exit 1
+fi
+
+RULESET="flush ruleset
+create table inet filter
+set inet filter foo {}
+add element inet filter foo { foobar }"
+
 $NFT -f - <<< $RULESET || exit 0