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s390/keyboard: avoid off-by-one when using strnlen_user()

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strnlen_user() returns the length of the string including terminating 0.
So avoid counting it again and unnecessarily reducing maximum string
size by 1.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Jan Kara 2015-06-02 12:38:39 +02:00 committed by Martin Schwidefsky
parent 2e4aa2f2bd
commit 8cb81811e9
1 changed files with 8 additions and 5 deletions
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13
drivers/s390/char/keyboard.c
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@ -433,20 +433,23 @@ do_kdgkb_ioctl(struct kbd_data *kbd, struct kbsentry __user *u_kbs,
case KDSKBSENT:
if (!perm)
return -EPERM;
len = strnlen_user(u_kbs->kb_string,
sizeof(u_kbs->kb_string) - 1);
len = strnlen_user(u_kbs->kb_string, sizeof(u_kbs->kb_string));
if (!len)
return -EFAULT;
if (len > sizeof(u_kbs->kb_string) - 1)
if (len > sizeof(u_kbs->kb_string))
return -EINVAL;
p = kmalloc(len + 1, GFP_KERNEL);
p = kmalloc(len, GFP_KERNEL);
if (!p)
return -ENOMEM;
if (copy_from_user(p, u_kbs->kb_string, len)) {
kfree(p);
return -EFAULT;
}
p[len] = 0;
/*
* Make sure the string is terminated by 0. User could have
* modified it between us running strnlen_user() and copying it.
*/
p[len - 1] = 0;
kfree(kbd->func_table[kb_func]);
kbd->func_table[kb_func] = p;
break;