[nft PATCH v3 2/4] mnl: Support simple wildcards in netdev hooks

[Phil Sutter <phil@xxxxxx>]

When building NFTA_FLOWTABLE_HOOK_DEVS, NFTA_HOOK_DEV or NFTA_HOOK_DEVS
attributes, detect trailing asterisks in interface names and reduce
attribute length accordingly. Kernel will use strncmp(), effectively
performing a prefix search this way.

Deserialization (i.e., appending asterisk to interface names which don't
include a trailing nul-char) happens in libnftnl.

Signed-off-by: Phil Sutter <phil@xxxxxx>
---
Changes since v2:
- Introduce mnl_attr_put_ifname() to perform the conditional
  mnl_attr_put() parameter adjustment
- Sanity-check array index in above function to avoid out-of-bounds
  access
---
 src/mnl.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/mnl.c b/src/mnl.c
index 43229f2498e55..8ec4ef40d2761 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -795,6 +795,17 @@ static void nft_dev_array_free(const struct nft_dev *dev_array)
 	free_const(dev_array);
 }
 
+static void mnl_attr_put_ifname(struct nlmsghdr *nlh,
+				int attr, const char *ifname)
+{
+	int len = strlen(ifname) + 1;
+
+	if (len >= 2 && ifname[len - 2] == '*')
+		len -= 2;
+
+	mnl_attr_put(nlh, attr, len, ifname);
+}
+
 static void mnl_nft_chain_devs_build(struct nlmsghdr *nlh, struct cmd *cmd)
 {
 	const struct expr *dev_expr = cmd->chain->dev_expr;
@@ -805,12 +816,13 @@ static void mnl_nft_chain_devs_build(struct nlmsghdr *nlh, struct cmd *cmd)
 	dev_array = nft_dev_array(dev_expr, &num_devs);
 	if (num_devs == 1) {
 		cmd_add_loc(cmd, nlh, dev_array[0].location);
-		mnl_attr_put_strz(nlh, NFTA_HOOK_DEV, dev_array[0].ifname);
+		mnl_attr_put_ifname(nlh, NFTA_HOOK_DEV, dev_array[0].ifname);
 	} else {
 		nest_dev = mnl_attr_nest_start(nlh, NFTA_HOOK_DEVS);
 		for (i = 0; i < num_devs; i++) {
 			cmd_add_loc(cmd, nlh, dev_array[i].location);
-			mnl_attr_put_strz(nlh, NFTA_DEVICE_NAME, dev_array[i].ifname);
+			mnl_attr_put_ifname(nlh, NFTA_DEVICE_NAME,
+					    dev_array[i].ifname);
 		}
 		mnl_attr_nest_end(nlh, nest_dev);
 	}
@@ -2085,13 +2097,13 @@ static void mnl_nft_ft_devs_build(struct nlmsghdr *nlh, struct cmd *cmd)
 	const struct expr *dev_expr = cmd->flowtable->dev_expr;
 	const struct nft_dev *dev_array;
 	struct nlattr *nest_dev;
-	int i, num_devs= 0;
+	int i, num_devs = 0;
 
 	dev_array = nft_dev_array(dev_expr, &num_devs);
 	nest_dev = mnl_attr_nest_start(nlh, NFTA_FLOWTABLE_HOOK_DEVS);
 	for (i = 0; i < num_devs; i++) {
 		cmd_add_loc(cmd, nlh, dev_array[i].location);
-		mnl_attr_put_strz(nlh, NFTA_DEVICE_NAME, dev_array[i].ifname);
+		mnl_attr_put_ifname(nlh, NFTA_DEVICE_NAME, dev_array[i].ifname);
 	}
 
 	mnl_attr_nest_end(nlh, nest_dev);
-- 
2.49.0