vt: keyboard, simplify vt_kdgkbsent

commit 6ca03f90527e499dd5e32d6522909e2ad390896b upstream.

Use 'strlen' of the string, add one for NUL terminator and simply do
'copy_to_user' instead of the explicit 'for' loop. This makes the
KDGKBSENT case more compact.

The only thing we need to take care about is NULL 'func_table[i]'. Use
an empty string in that case.

The original check for overflow could never trigger as the func_buf
strings are always shorter or equal to 'struct kbsentry's.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20201019085517.10176-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 610cb8338d5350951e605f347dce67066d2fe19c..48ace80765d8874e5a6b4a0f8bf0d2e4251052dc 100644 (file)
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1963,9 +1963,7 @@ out:
 int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
 {
        struct kbsentry *kbs;
-       char *p;
        u_char *q;
-       u_char __user *up;
        int sz, fnw_sz;
        int delta;
        char *first_free, *fj, *fnw;
@@ -1991,23 +1989,15 @@ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm)
        i = kbs->kb_func;
 
        switch (cmd) {
-       case KDGKBSENT:
-               sz = sizeof(kbs->kb_string) - 1; /* sz should have been
-                                                 a struct member */
-               up = user_kdgkb->kb_string;
-               p = func_table[i];
-               if(p)
-                       for ( ; *p && sz; p++, sz--)
-                               if (put_user(*p, up++)) {
-                                       ret = -EFAULT;
-                                       goto reterr;
-                               }
-               if (put_user('\0', up)) {
-                       ret = -EFAULT;
-                       goto reterr;
-               }
-               kfree(kbs);
-               return ((p && *p) ? -EOVERFLOW : 0);
+       case KDGKBSENT: {
+               /* size should have been a struct member */
+               unsigned char *from = func_table[i] ? : "";
+
+               ret = copy_to_user(user_kdgkb->kb_string, from,
+                               strlen(from) + 1) ? -EFAULT : 0;
+
+               goto reterr;
+       }
        case KDSKBSENT:
                if (!perm) {
                        ret = -EPERM;