vt: Clear selection before changing the font

When changing the console font with ioctl(KDFONTOP) the new font size
can be bigger than the previous font. A previous selection may thus now
be outside of the new screen size and thus trigger out-of-bounds
accesses to graphics memory if the selection is removed in
vc_do_resize().

Prevent such out-of-memory accesses by dropping the selection before the
various con_font_set() console handlers are called.

Reported-by: syzbot+14b0e8f3fd1612e35350@syzkaller.appspotmail.com
Cc: stable <stable@kernel.org>
Tested-by: Khalid Masum <khalid.masum.92@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
Link: https://lore.kernel.org/r/YuV9apZGNmGfjcor@p100
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index ae9c926..0b669c8 100644 (file)
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -4662,9 +4662,11 @@ static int con_font_set(struct vc_data *vc, struct console_font_op *op)
        console_lock();
        if (vc->vc_mode != KD_TEXT)
                rc = -EINVAL;
-       else if (vc->vc_sw->con_font_set)
+       else if (vc->vc_sw->con_font_set) {
+               if (vc_is_sel(vc))
+                       clear_selection();
                rc = vc->vc_sw->con_font_set(vc, &font, op->flags);
-       else
+       } else
                rc = -ENOSYS;
        console_unlock();
        kfree(font.data);
@@ -4691,9 +4693,11 @@ static int con_font_default(struct vc_data *vc, struct console_font_op *op)
                console_unlock();
                return -EINVAL;
        }
-       if (vc->vc_sw->con_font_default)
+       if (vc->vc_sw->con_font_default) {
+               if (vc_is_sel(vc))
+                       clear_selection();
                rc = vc->vc_sw->con_font_default(vc, &font, s);
-       else
+       } else
                rc = -ENOSYS;
        console_unlock();
        if (!rc) {