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

[Laurijssen <lauserve@gmail.com>]

- add utsname_set_field to utsname_sysctl.c, it reuses duplicated code
- call utsname_set_field from sethostname/setdomainname
- moved uts_proc_notify from .h into utsname_sysctl.c and turned static

Signed-off-by: Laurijssen <laurijssen@protonmail.com>
---
 include/linux/utsname.h | 10 ++----
 kernel/sys.c            | 46 ++-----------------------
 kernel/utsname_sysctl.c | 75 ++++++++++++++++++++++++++++++++++-------
 3 files changed, 66 insertions(+), 65 deletions(-)

diff --git a/include/linux/utsname.h b/include/linux/utsname.h
index dc5594ffffcc..409261d5381f 100644
--- a/include/linux/utsname.h
+++ b/include/linux/utsname.h
@@ -18,14 +18,6 @@ enum uts_proc {
 	UTS_PROC_DOMAINNAME,
 };
 
-#ifdef CONFIG_SYSCTL
-extern void uts_proc_notify(enum uts_proc proc);
-#else
-static inline void uts_proc_notify(enum uts_proc proc)
-{
-}
-#endif
-
 static inline struct new_utsname *utsname(void)
 {
 	return &current->nsproxy->uts_ns->name;
@@ -38,4 +30,6 @@ static inline struct new_utsname *init_utsname(void)
 
 extern struct rw_semaphore uts_sem;
 
+int utsname_set_field(char __user *name, int len, enum uts_proc proc);
+
 #endif /* _LINUX_UTSNAME_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 755bfa5ccd92..688c5e9e222f 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1421,28 +1421,7 @@ SYSCALL_DEFINE1(olduname, struct oldold_utsname __user *, name)
 
 SYSCALL_DEFINE2(sethostname, 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->nodename, tmp, len);
-		memset(u->nodename + len, 0, sizeof(u->nodename) - len);
-		errno = 0;
-		uts_proc_notify(UTS_PROC_HOSTNAME);
-		up_write(&uts_sem);
-	}
-	return errno;
+	return utsname_set_field(name, len, UTS_PROC_HOSTNAME);
 }
 
 #ifdef __ARCH_WANT_SYS_GETHOSTNAME
@@ -1475,28 +1454,7 @@ 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 */
diff --git a/kernel/utsname_sysctl.c b/kernel/utsname_sysctl.c
index 6c1522201e39..026e5c877a8b 100644
--- a/kernel/utsname_sysctl.c
+++ b/kernel/utsname_sysctl.c
@@ -5,6 +5,7 @@
  *  Author: Eric Biederman <ebiederm@xmision.com>
  */
 
+#include <linux/capability.h>
 #include <linux/export.h>
 #include <linux/uts.h>
 #include <linux/utsname.h>
@@ -12,6 +13,9 @@
 #include <linux/sysctl.h>
 #include <linux/wait.h>
 #include <linux/rwsem.h>
+#include <linux/uaccess.h>
+
+static const struct ctl_table uts_kern_table[];
 
 #ifdef CONFIG_SYSCTL
 
@@ -67,10 +71,68 @@ static int proc_do_uts_string(const struct ctl_table *table, int write,
 
 	return r;
 }
+
+/*
+ * Notify userspace about a change in a certain entry of uts_kern_table,
+ * identified by the parameter proc.
+ */
+static void uts_proc_notify(enum uts_proc proc)
+{
+	const struct ctl_table *table = &uts_kern_table[proc];
+
+	proc_sys_poll_notify(table->poll);
+}
 #else
 #define proc_do_uts_string NULL
+
+static inline void uts_proc_notify(enum uts_proc proc)
+{
+}
 #endif
 
+int utsname_set_field(char __user *name, int len, enum uts_proc proc)
+{
+	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;
+		char *field;
+
+		add_device_randomness(tmp, len);
+		down_write(&uts_sem);
+
+		u = utsname();
+
+		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(proc);
+		up_write(&uts_sem);
+	}
+	return errno;
+}
+
 static DEFINE_CTL_TABLE_POLL(hostname_poll);
 static DEFINE_CTL_TABLE_POLL(domainname_poll);
 
@@ -122,19 +184,6 @@ static const struct ctl_table uts_kern_table[] = {
 	},
 };
 
-#ifdef CONFIG_SYSCTL
-/*
- * Notify userspace about a change in a certain entry of uts_kern_table,
- * identified by the parameter proc.
- */
-void uts_proc_notify(enum uts_proc proc)
-{
-	const struct ctl_table *table = &uts_kern_table[proc];
-
-	proc_sys_poll_notify(table->poll);
-}
-#endif
-
 static int __init utsname_sysctl_init(void)
 {
 	register_sysctl("kernel", uts_kern_table);
-- 
2.53.0