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

[Laurijssen <lauserve@gmail.com>]

Changes after review, cleanup of duplicated code in sethostname and
setdomainname.

- add static utsname_set_field sys.c
- call utsname_set_field from sethostname/setdomainname
- code compiles now when CONFIG_SYSCTL is not defined

Signed-off-by: Laurijssen <laurijssen@protonmail.com>
---
 kernel/sys.c | 53 ++++++++++++++++++++++++++--------------------------
 1 file changed, 27 insertions(+), 26 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 755bfa5ccd92..77fedd127a3f 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1419,7 +1419,7 @@ SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
 }
 #endif
 
-SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
+static int utsname_set_field(char __user *name, int len, enum uts_proc proc)
 {
 	int errno;
 	char tmp[__NEW_UTS_LEN];
@@ -1432,19 +1432,41 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
 	errno = -EFAULT;
 	if (!copy_from_user(tmp, name, len)) {
 		struct new_utsname *u;
+		char *field;
 
 		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);
+
+		switch (proc) {
+		case UTS_PROC_HOSTNAME:
+			field = u->nodename;
+			break;
+		case UTS_PROC_DOMAINNAME:
+			field = u->domainname;
+			break;
+		default:
+			WARN_ON_ONCE(1);
+			field = u->domainname;
+			break;
+		}
+
+		memcpy(field, tmp, len);
+		memset(field + len, 0, sizeof_field(struct new_utsname, nodename) - len);
+
 		errno = 0;
-		uts_proc_notify(UTS_PROC_HOSTNAME);
+		uts_proc_notify(proc);
 		up_write(&uts_sem);
 	}
 	return errno;
 }
 
+SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
+{
+	return utsname_set_field(name, len, UTS_PROC_HOSTNAME);
+}
+
 #ifdef __ARCH_WANT_SYS_GETHOSTNAME
 
 SYSCALL_DEFINE2(gethostname, char __user *, name, int, len)
@@ -1475,28 +1497,7 @@ 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;
-
-		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 utsname_set_field(name, len, UTS_PROC_DOMAINNAME);
 }
 
 /* make sure you are allowed to change @tsk limits before calling this */
-- 
2.53.0