linux-kernel - [PATCH net-next] af_unix: Refine UNIX domain sockets autobind identifier length

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Message-Id: <20250205060653.2221165-1-buaajxlj@163.com>
Date: Wed,  5 Feb 2025 14:06:53 +0800
From: Liang Jie <buaajxlj@....com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>,
	Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Michal Luczaj <mhal@...x.co>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Liang Jie <liangjie@...iang.com>
Subject: [PATCH net-next] af_unix: Refine UNIX domain sockets autobind identifier length

From: Liang Jie <liangjie@...iang.com>

Refines autobind identifier length for UNIX domain sockets, addressing
issues of memory waste and code readability.

The previous implementation in the unix_autobind function of UNIX domain
sockets used hardcoded values such as 16, 6, and 5 for memory allocation
and setting the length of the autobind identifier, which was not only
inflexible but also led to reduced code clarity. Additionally, allocating
16 bytes of memory for the autobind path was excessive, given that only 6
bytes were ultimately used.

To mitigate these issues, introduces the following changes:
 - A new macro AUTOBIND_LEN is defined to clearly represent the total
   length of the autobind identifier, which improves code readability and
   maintainability. It is set to 6 bytes to accommodate the unique autobind
   process identifier.
 - Memory allocation for the autobind path is now precisely based on
   AUTOBIND_LEN, thereby preventing memory waste.
 - The sprintf() function call is updated to dynamically format the
   autobind identifier according to the defined length, further enhancing
   code consistency and readability.

The modifications result in a leaner memory footprint and elevated code
quality, ensuring that the functional aspect of autobind behavior in UNIX
domain sockets remains intact.

Signed-off-by: Liang Jie <liangjie@...iang.com>
---
 net/unix/af_unix.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 34945de1fb1f..5dcc55f2e3a1 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1186,6 +1186,13 @@ static struct sock *unix_find_other(struct net *net,
 	return sk;
 }
 
+/*
+ * Define the total length of the autobind identifier for UNIX domain sockets.
+ * - The first byte distinguishes abstract sockets from filesystem-based sockets.
+ * - The subsequent five bytes store a unique identifier for the autobinding process.
+ */
+#define AUTOBIND_LEN 6
+
 static int unix_autobind(struct sock *sk)
 {
 	struct unix_sock *u = unix_sk(sk);
@@ -1204,11 +1211,11 @@ static int unix_autobind(struct sock *sk)
 
 	err = -ENOMEM;
 	addr = kzalloc(sizeof(*addr) +
-		       offsetof(struct sockaddr_un, sun_path) + 16, GFP_KERNEL);
+		       offsetof(struct sockaddr_un, sun_path) + AUTOBIND_LEN, GFP_KERNEL);
 	if (!addr)
 		goto out;
 
-	addr->len = offsetof(struct sockaddr_un, sun_path) + 6;
+	addr->len = offsetof(struct sockaddr_un, sun_path) + AUTOBIND_LEN;
 	addr->name->sun_family = AF_UNIX;
 	refcount_set(&addr->refcnt, 1);
 
@@ -1217,7 +1224,7 @@ static int unix_autobind(struct sock *sk)
 	lastnum = ordernum & 0xFFFFF;
 retry:
 	ordernum = (ordernum + 1) & 0xFFFFF;
-	sprintf(addr->name->sun_path + 1, "%05x", ordernum);
+	sprintf(addr->name->sun_path + 1, "%0*x", AUTOBIND_LEN - 1, ordernum);
 
 	new_hash = unix_abstract_hash(addr->name, addr->len, sk->sk_type);
 	unix_table_double_lock(net, old_hash, new_hash);
-- 
2.25.1