[PATCH libftnl 03/12] src: move several MNL_STRING types to MNL_NUL_STRING

[Florian Westphal <fw@strlen.de>]

LLM finding:
mnl_attr_get_str() returns a pointer into a fixed-length TLV payload with
no guaranteed NUL terminator.

This is the classic 'NLA_STRING' vs. 'NUL_STRING'.
libmnl only checks for terminating NUL when asked to validate a
NUL_STRING attribute.  As we parse nf_tables data coming from kernel,
we can actually rely on the kernel including the terminating NUL
character for us, even for NLA_STRING.

Just switch those affected attributes (strdup() after
mnl_attr_validate(... MNL_STRING) to MNL_NUL_STRING.

This doesn't break any existing users, closes the finding and
hardens future users that might parse netlink attributes coming
from a different source than the kernel.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/chain.c         | 2 +-
 src/expr/data_reg.c | 2 +-
 src/set.c           | 2 +-
 src/utils.c         | 5 +++--
 4 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/chain.c b/src/chain.c
index 13b0231ee345..c72505c22e17 100644
--- a/src/chain.c
+++ b/src/chain.c
@@ -613,7 +613,7 @@ static int nftnl_chain_parse_hook_cb(const struct nlattr *attr, void *data)
 			abi_breakage();
 		break;
 	case NFTA_HOOK_DEV:
-		if (mnl_attr_validate(attr, MNL_TYPE_STRING) < 0)
+		if (mnl_attr_validate(attr, MNL_TYPE_NUL_STRING) < 0)
 			abi_breakage();
 		break;
 	}
diff --git a/src/expr/data_reg.c b/src/expr/data_reg.c
index 0a1c0bdee6c2..e38e493f0592 100644
--- a/src/expr/data_reg.c
+++ b/src/expr/data_reg.c
@@ -155,7 +155,7 @@ static int nftnl_verdict_parse_cb(const struct nlattr *attr, void *data)
 			abi_breakage();
 		break;
 	case NFTA_VERDICT_CHAIN:
-		if (mnl_attr_validate(attr, MNL_TYPE_STRING) < 0)
+		if (mnl_attr_validate(attr, MNL_TYPE_NUL_STRING) < 0)
 			abi_breakage();
 		break;
 	}
diff --git a/src/set.c b/src/set.c
index f7b0526253ff..22fd4a839f80 100644
--- a/src/set.c
+++ b/src/set.c
@@ -491,7 +491,7 @@ static int nftnl_set_parse_attr_cb(const struct nlattr *attr, void *data)
 	case NFTA_SET_TABLE:
 	case NFTA_SET_NAME:
 	case NFTA_SET_TYPE:
-		if (mnl_attr_validate(attr, MNL_TYPE_STRING) < 0)
+		if (mnl_attr_validate(attr, MNL_TYPE_NUL_STRING) < 0)
 			abi_breakage();
 		break;
 	case NFTA_SET_HANDLE:
diff --git a/src/utils.c b/src/utils.c
index f7d035baa3ae..95a252ed44f3 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -200,14 +200,15 @@ void nftnl_attr_put_ifname(struct nlmsghdr *nlh, const char *ifname)
 
 char *nftnl_attr_get_ifname(const struct nlattr *attr)
 {
+	uint16_t dlen = mnl_attr_get_payload_len(attr);
 	const char *dev = mnl_attr_get_str(attr);
 	char buf[IFNAMSIZ];
 
 	switch (mnl_attr_get_type(attr)) {
 	case NFTA_DEVICE_NAME:
-		return strdup(dev);
+		return strndup(dev, dlen);
 	case NFTA_DEVICE_PREFIX:
-		snprintf(buf, IFNAMSIZ, "%s*", dev);
+		snprintf(buf, IFNAMSIZ, "%.*s*", (int)dlen, dev);
 		return strdup(buf);
 	default:
 		return NULL;
-- 
2.55.0