Re: [PATCH nft] segtree: fix string data initialisation

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Wed, Mar 05, 2025 at 04:01:48PM +0100, Florian Westphal wrote:
> This uses the wrong length.  This must re-use the length of the datatype,
> not the string length.
> 
> The added test cases will fail without the fix due to erroneous
> overlap detection, which in itself is due to incorrect sorting of
> the elements.
> 
> Example error:
>  netlink: Error: interval overlaps with an existing one
>  add element inet testifsets simple_wild {  "2-1" } failed.
>  table inet testifsets {
>       ...       elements = { "1-1", "abcdef*", "othername", "ppp0" }
> 
> ... but clearly "2-1" doesn't overlap with any existing members.
> The false detection is because of the "acvdef*" wildcard getting sorted
> at the beginning of the list which is because its erronously initialised
> as a 64bit number instead of 128 bits (16 bytes / IFNAMSIZ).

One question here.

> Fixes: 5e393ea1fc0a ("segtree: add string "range" reversal support")
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  src/segtree.c                                |  2 +-
>  tests/shell/testcases/sets/sets_with_ifnames | 62 ++++++++++++++++++++
>  2 files changed, 63 insertions(+), 1 deletion(-)
> 
> diff --git a/src/segtree.c b/src/segtree.c
> index 2e32a3291979..11cf27c55dcb 100644
> --- a/src/segtree.c
> +++ b/src/segtree.c
> @@ -471,7 +471,7 @@ static struct expr *interval_to_string(struct expr *low, struct expr *i, const m
>  
>  	expr = constant_expr_alloc(&low->location, low->dtype,
>  				   BYTEORDER_HOST_ENDIAN,
> -				   (str_len + 1) * BITS_PER_BYTE, data);
> +				   len * BITS_PER_BYTE, data);

BTW, is this also needed?

diff --git a/src/segtree.c b/src/segtree.c
index 2e32a3291979..b7a89383fae0 100644
--- a/src/segtree.c
+++ b/src/segtree.c
@@ -453,7 +453,7 @@ static struct expr *interval_to_string(struct expr *low, struct expr *i, const m
 {
        unsigned int len = div_round_up(i->len, BITS_PER_BYTE);
        unsigned int prefix_len, str_len;
-       char data[len + 2];
+       char data[len + 2] = {};
        struct expr *expr;
 
        prefix_len = expr_value(i)->len - mpz_scan0(range, 0);

otherwise uninitialized data could be send to the kernel?

>  	return __expr_to_set_elem(low, expr);
>  }
> diff --git a/tests/shell/testcases/sets/sets_with_ifnames b/tests/shell/testcases/sets/sets_with_ifnames
> index a4bc5072938e..c65499b76bc5 100755
> --- a/tests/shell/testcases/sets/sets_with_ifnames
> +++ b/tests/shell/testcases/sets/sets_with_ifnames
> @@ -105,10 +105,67 @@ check_matching_icmp_ppp()
>  	fi
>  }
>  
> +check_add_del_ifnames()
> +{
> +	local what="$1"
> +	local setname="$2"
> +	local prefix="$3"
> +	local data="$4"
> +	local i=0
> +
> +	for i in $(seq 1 5);do
> +		local cmd="element inet testifsets $setname { "
> +		local to_batch=16
> +
> +		for j in $(seq 1 $to_batch);do
> +			local name=$(printf '"%x-%d"' $i $j)
> +
> +			[ -n "$prefix" ] && cmd="$cmd $prefix . "
> +
> +			cmd="$cmd $name"
> +
> +			[ -n "$data" ] && cmd="$cmd : $data"
> +
> +			if [ $j -lt $to_batch ] ; then
> +				cmd="$cmd, "
> +			fi
> +		done
> +
> +		cmd="$cmd }"
> +
> +		if ! $NFT "$what" "$cmd"; then
> +			echo "$what $cmd failed."
> +			$NFT list set inet testifsets $setname
> +			exit 1
> +		fi
> +
> +		if ! ip netns exec "$ns1" $NFT "$what" "$cmd"; then
> +			echo "$ns1 $what $cmd failed."
> +			ip netns exec "$ns1" $NFT list set inet testifsets $setname
> +			exit 1
> +		fi
> +	done
> +}
> +
> +check_add_ifnames()
> +{
> +	check_add_del_ifnames "add" "$1" "$2" "$3"
> +}
> +
> +check_del_ifnames()
> +{
> +	check_add_del_ifnames "delete" "$1" "$2" "$3"
> +}
> +
>  ip netns add "$ns1" || exit 111
>  ip netns add "$ns2" || exit 111
>  ip netns exec "$ns1" $NFT -f "$dumpfile" || exit 3
>  
> +check_add_ifnames "simple" "" ""
> +check_add_ifnames "simple_wild" "" ""
> +check_add_ifnames "concat" "10.1.2.2" ""
> +check_add_ifnames "map_wild" "" "drop"
> +
>  for n in abcdef0 abcdef1 othername;do
>  	check_elem simple $n
>  done
> @@ -150,3 +207,8 @@ ip -net "$ns2" addr add 10.1.2.2/24 dev veth0
>  ip -net "$ns2" addr add 10.2.2.2/24 dev veth1
>  
>  check_matching_icmp_ppp
> +
> +check_del_ifnames "simple" "" ""
> +check_del_ifnames "simple_wild" "" ""
> +check_del_ifnames "concat" "10.1.2.2" ""
> +check_del_ifnames "map_wild" "" "drop"
> -- 
> 2.48.1
> 
>