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

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