[PATCH] add setutsname to reuse code in setdomainname and sethostname

[Laurijssen <lauserve@gmail.com>]

- sethostname and setdomainname duplicated code with one field difference.
- added setutsname with arguments domainname/hostname to reuse the same code.

Signed-off-by: Laurijssen <laurijssen@protonmail.com>
---
 kernel/sys.c | 46 ++++++++++++++++++----------------------------
 1 file changed, 18 insertions(+), 28 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 755bfa5ccd92..3a4e483c22d5 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1419,7 +1419,9 @@ SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
 }
 #endif
 
-SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
+static int setutsname(char __user *name, int len, enum uts_proc uts_proc,
+		      char (*field)[__NEW_UTS_LEN + 1],
+		      int fieldlen)
 {
 	int errno;
 	char tmp[__NEW_UTS_LEN];
@@ -1431,20 +1433,26 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
 		return -EINVAL;
 	errno = -EFAULT;
 	if (!copy_from_user(tmp, name, len)) {
-		struct new_utsname *u;
-
 		add_device_randomness(tmp, len);
 		down_write(&uts_sem);
-		u = utsname();
-		memcpy(u->nodename, tmp, len);
-		memset(u->nodename + len, 0, sizeof(u->nodename) - len);
+		memcpy(*field, tmp, len);
+		memset(*field + len, 0, fieldlen - len);
+
 		errno = 0;
-		uts_proc_notify(UTS_PROC_HOSTNAME);
+		uts_proc_notify(uts_proc);
 		up_write(&uts_sem);
 	}
 	return errno;
 }
 
+SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
+{
+	// utsname() always returns a valid pointer to the current utsname structure.
+	struct new_utsname *u = utsname();
+
+	return setutsname(name, len, UTS_PROC_HOSTNAME, &u->nodename, sizeof(u->nodename));
+}
+
 #ifdef __ARCH_WANT_SYS_GETHOSTNAME
 
 SYSCALL_DEFINE2(gethostname, char __user *, name, int, len)
@@ -1475,28 +1483,10 @@ SYSCALL_DEFINE2(gethostname, char __user *, name, int, len)
  */
 SYSCALL_DEFINE2(setdomainname, char __user *, name, int, len)
 {
-	int errno;
-	char tmp[__NEW_UTS_LEN];
-
-	if (!ns_capable(current->nsproxy->uts_ns->user_ns, CAP_SYS_ADMIN))
-		return -EPERM;
-	if (len < 0 || len > __NEW_UTS_LEN)
-		return -EINVAL;
-
-	errno = -EFAULT;
-	if (!copy_from_user(tmp, name, len)) {
-		struct new_utsname *u;
+	// utsname() always returns a valid pointer to the current utsname structure.
+	struct new_utsname *u = utsname();
 
-		add_device_randomness(tmp, len);
-		down_write(&uts_sem);
-		u = utsname();
-		memcpy(u->domainname, tmp, len);
-		memset(u->domainname + len, 0, sizeof(u->domainname) - len);
-		errno = 0;
-		uts_proc_notify(UTS_PROC_DOMAINNAME);
-		up_write(&uts_sem);
-	}
-	return errno;
+	return setutsname(name, len, UTS_PROC_DOMAINNAME, &u->domainname, sizeof(u->domainname));
 }
 
 /* make sure you are allowed to change @tsk limits before calling this */
-- 
2.53.0