[PATCH net-next v2] af_unix: Refine UNIX pathname sockets autobind identifier length

[Liang Jie]

From: Liang Jie <liangjie@xxxxxxxxxxx>

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

The previous implementation in the unix_autobind function of UNIX pathname
sockets used hardcoded values such as 16 and 6 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 UNIX_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
   UNIX_AUTOBIND_LEN, thereby preventing memory waste.
 - To avoid buffer overflow and ensure that only the intended number of
   bytes are written, sprintf is replaced by snprintf with the proper
   buffer size set explicitly.

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

Signed-off-by: Liang Jie <liangjie@xxxxxxxxxxx>
Suggested-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
---

Changes in v2:
 - Removed the comments describing AUTOBIND_LEN.
 - Renamed the macro AUTOBIND_LEN to UNIX_AUTOBIND_LEN for clarity and
   specificity.
 - Corrected the buffer length in snprintf to prevent potential buffer
   overflow issues.
 - Addressed warning from checkpatch.
 - Link to v1: https://lore.kernel.org/all/20250205060653.2221165-1-buaajxlj@xxxxxxx/

 net/unix/af_unix.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 34945de1fb1f..6c449f78f0a6 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1186,6 +1186,8 @@ static struct sock *unix_find_other(struct net *net,
 	return sk;
 }
 
+#define UNIX_AUTOBIND_LEN 6
+
 static int unix_autobind(struct sock *sk)
 {
 	struct unix_sock *u = unix_sk(sk);
@@ -1203,12 +1205,12 @@ static int unix_autobind(struct sock *sk)
 		goto out;
 
 	err = -ENOMEM;
-	addr = kzalloc(sizeof(*addr) +
-		       offsetof(struct sockaddr_un, sun_path) + 16, GFP_KERNEL);
+	addr = kzalloc(sizeof(*addr) + offsetof(struct sockaddr_un, sun_path) +
+			UNIX_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) + UNIX_AUTOBIND_LEN;
 	addr->name->sun_family = AF_UNIX;
 	refcount_set(&addr->refcnt, 1);
 
@@ -1217,7 +1219,7 @@ static int unix_autobind(struct sock *sk)
 	lastnum = ordernum & 0xFFFFF;
 retry:
 	ordernum = (ordernum + 1) & 0xFFFFF;
-	sprintf(addr->name->sun_path + 1, "%05x", ordernum);
+	snprintf(addr->name->sun_path + 1, 5, "%05x", 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