vt/vgacon: Check if screen resize request comes from userspace

Various console drivers are able to resize the screen via the con_resize()
hook.  This hook is also visible in userspace via the TIOCWINSZ, VT_RESIZE and
VT_RESIZEX ioctl's.  One particular utility, SVGATextMode, expects that
con_resize() of the VGA console will always return success even if the
resulting screen is not compatible with the hardware.  However, this
particular behavior of the VGA console, as reported in Kernel Bugzilla Bug
7513, can cause undefined behavior if the user starts with a console size
larger than 80x25.

To work around this problem, add an extra parameter to con_resize().  This
parameter is ignored by drivers except for vgacon.  If this parameter is
non-zero, then the resize request came from a VT_RESIZE or VT_RESIZEX ioctl
and vgacon will always return success.  If this parameter is zero, vgacon will
return -EINVAL if the requested size is not compatible with the hardware.  The
latter is the more correct behavior.

With this change, SVGATextMode should still work correctly while in-kernel and
stty resize calls can expect correct behavior from vgacon.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
index dc77fed7b285..d71f7c0f931b 100644
--- a/include/linux/console_struct.h
+++ b/include/linux/console_struct.h
@@ -100,6 +100,7 @@ struct vc_data {
         unsigned char   vc_G1_charset;
         unsigned char   vc_saved_G0;
         unsigned char   vc_saved_G1;
+        unsigned int    vc_resize_user;         /* resize request from user */
         unsigned int    vc_bell_pitch;          /* Console bell pitch */
         unsigned int    vc_bell_duration;       /* Console bell duration */
         struct vc_data **vc_display_fg;         /* [!] Ptr to var holding fg console for this display */