src: Don't parse string as verdict in map

In verdict map, string values are accidentally treated as verdicts.

For example:

table t {
    map foo {
        type ipv4_addr : verdict
        elements = {
            192.168.0.1 : bar
        }
    }
    chain output {
        type filter hook output priority mangle;
        ip daddr vmap @foo
    }
}

Though "bar" is not a valid verdict (should be "jump bar" or something),
the string is taken as the element value. Then NFTA_DATA_VALUE is sent
to the kernel instead of NFTA_DATA_VERDICT. This would be rejected by
recent kernels. On older ones (e.g. v5.4.x) that don't validate the
type, a warning can be seen when the rule is hit, because of the
corrupted verdict value:

[5120263.467627] WARNING: CPU: 12 PID: 303303 at net/netfilter/nf_tables_core.c:229 nft_do_chain+0x394/0x500 [nf_tables]

Indeed, we don't parse verdicts during evaluation, but only chain names,
which is of type string rather than verdict. For example, "jump $var" is
a verdict while "$var" is a string.

Fixes: c64457cff967 ("src: Allow goto and jump to a variable")
Signed-off-by: Xiao Liang <shaw.leon@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/shell/testcases/nft-f/0031vmap_string_0 b/tests/shell/testcases/nft-f/0031vmap_string_0
new file mode 100755
index 00000000..2af846a4
--- /dev/null
+++ b/tests/shell/testcases/nft-f/0031vmap_string_0
@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# Tests parse of corrupted verdicts
+
+set -e
+
+RULESET="
+table ip foo {
+	map bar {
+		type ipv4_addr : verdict
+		elements = {
+			192.168.0.1 : ber
+		}
+	}
+
+	chain ber {
+	}
+}"
+
+$NFT -f - <<< "$RULESET" && exit 1
+exit 0