[PATCH 4.14 084/125] vt: keyboard, simplify vt_kdgkbsent

Greg Kroah-Hartman
2020-11-03T21:11:55Z

From: Jiri Slaby <jslaby@suse.cz>

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>

---
drivers/tty/vt/keyboard.c | 28 +++++++++-------------------
1 file changed, 9 insertions(+), 19 deletions(-)

--- 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 kb
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;