linux-hardening - [PATCH 2/7] netfilter: nf_tables: refactor deprecated strncpy

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Date:   Tue, 08 Aug 2023 22:48:07 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-hardening@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH 2/7] netfilter: nf_tables: refactor deprecated strncpy

Prefer `strscpy` over `strncpy`.

Signed-off-by: Justin Stitt <justinstitt@...gle.com>

---
Note:
It is hard to tell if there was a bug here in the first place but it's better
to use a more robust and less ambiguous interface anyways.

`helper->name` has a size of 16 and the 3rd argument to `strncpy`
(NF_CT_HELPER_LEN) is also 16. This means that depending on where
`dest`'s offset is relative to `regs->data` which has a length of 20,
there may be a chance the dest buffer ends up non NUL-terminated. This
is probably fine though as the destination buffer in this case may be
fine being non NUL-terminated. If this is the case, we should probably
opt for `strtomem` instead of `strscpy`.
---
 net/netfilter/nft_ct.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c
index 38958e067aa8..10126559038b 100644
--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -108,7 +108,7 @@ static void nft_ct_get_eval(const struct nft_expr *expr,
 		helper = rcu_dereference(help->helper);
 		if (helper == NULL)
 			goto err;
-		strncpy((char *)dest, helper->name, NF_CT_HELPER_NAME_LEN);
+		strscpy((char *)dest, helper->name, NF_CT_HELPER_NAME_LEN);
 		return;
 #ifdef CONFIG_NF_CONNTRACK_LABELS
 	case NFT_CT_LABELS: {

-- 
2.41.0.640.ga95def55d0-goog