netdev - [PATCH net-next 2/9] netfilter: nf_tables: replace deprecated strncpy with strscpy

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Message-Id: <20241014111420.29127-3-pablo@netfilter.org>
Date: Mon, 14 Oct 2024 13:14:13 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: netfilter-devel@...r.kernel.org
Cc: davem@...emloft.net,
	netdev@...r.kernel.org,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	fw@...len.de
Subject: [PATCH net-next 2/9] netfilter: nf_tables: replace deprecated strncpy with strscpy_pad

From: Justin Stitt <justinstitt@...gle.com>

strncpy() is deprecated for use on NUL-terminated destination strings [1] and
as such we should prefer more robust and less ambiguous string interfaces.

In this particular instance, the usage of strncpy() is fine and works as
expected. However, towards the goal of [2], we should consider replacing
it with an alternative as many instances of strncpy() are bug-prone. Its
removal from the kernel promotes better long term health for the
codebase.

The current usage of strncpy() likely just wants the NUL-padding
behavior offered by strncpy() and doesn't care about the
NUL-termination. Since the compiler doesn't know the size of @dest, we
can't use strtomem_pad(). Instead, use strscpy_pad() which behaves
functionally the same as strncpy() in this context -- as we expect
br_dev->name to be NUL-terminated itself.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90 [2]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Cc: Kees Cook <keescook@...omium.org>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
Reviewed-by: Simon Horman <horms@...nel.org>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/bridge/netfilter/nft_meta_bridge.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bridge/netfilter/nft_meta_bridge.c b/net/bridge/netfilter/nft_meta_bridge.c
index d12a221366d6..5adced1e7d0c 100644
--- a/net/bridge/netfilter/nft_meta_bridge.c
+++ b/net/bridge/netfilter/nft_meta_bridge.c
@@ -63,7 +63,7 @@ static void nft_meta_bridge_get_eval(const struct nft_expr *expr,
 		return nft_meta_get_eval(expr, regs, pkt);
 	}

-	strncpy((char *)dest, br_dev ? br_dev->name : "", IFNAMSIZ);
+	strscpy_pad((char *)dest, br_dev ? br_dev->name : "", IFNAMSIZ);
 	return;
 err:
 	regs->verdict.code = NFT_BREAK;
-- 
2.30.2