linux-kernel - [PATCH net-next v2] net: ipconfig: Replace strncpy with strscpy in ic_proto

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Message-ID: <20251126220804.102160-2-thorsten.blum@linux.dev>
Date: Wed, 26 Nov 2025 23:08:05 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: david laight <david.laight@...box.com>,
	"David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>
Cc: Thorsten Blum <thorsten.blum@...ux.dev>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH net-next v2] net: ipconfig: Replace strncpy with strscpy in ic_proto_name

strncpy() is deprecated [1] for NUL-terminated destination buffers
because it does not guarantee NUL termination. Replace it with strscpy()
to ensure the destination buffer is always NUL-terminated and to avoid
any additional NUL padding.

Although the identifier buffer has 252 usable bytes, strncpy() copied
only up to 251 bytes to the zero-initialized buffer, relying on the last
byte to act as an implicit NUL terminator. Switching to strscpy() avoids
this implicit behavior and does not use magic numbers.

The source string is also NUL-terminated and satisfies the
__must_be_cstr() requirement of strscpy().

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
---
Changes in v2:
- Use strscpy() to avoid unnecessary padding (David)
- Update patch title and description accordingly
- Link to v1: https://lore.kernel.org/lkml/20251126111358.64846-1-thorsten.blum@linux.dev/
---
 net/ipv4/ipconfig.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 22a7889876c1..019408d3ca2c 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -1690,7 +1690,8 @@ static int __init ic_proto_name(char *name)
 			*v = 0;
 			if (kstrtou8(client_id, 0, dhcp_client_identifier))
 				pr_debug("DHCP: Invalid client identifier type\n");
-			strncpy(dhcp_client_identifier + 1, v + 1, 251);
+			strscpy(dhcp_client_identifier + 1, v + 1,
+				sizeof(dhcp_client_identifier) - 1);
 			*v = ',';
 		}
 		return 1;
-- 
Thorsten Blum <thorsten.blum@...ux.dev>
GPG: 1D60 735E 8AEF 3BE4 73B6  9D84 7336 78FD 8DFE EAD4