[PATCH 02/17] vt/vgacon: Check if screen resize request comes from userspace

["Antonino A. Daplas" <adaplas@gmail.com>]

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>
---

 drivers/char/vt.c                       |   13 +++++++++----
 drivers/char/vt_ioctl.c                 |   15 +++++++++++++--
 drivers/usb/misc/sisusbvga/sisusb_con.c |    3 ++-
 drivers/video/console/fbcon.c           |    2 +-
 drivers/video/console/vgacon.c          |    7 ++++---
 include/linux/console.h                 |    3 ++-
 include/linux/console_struct.h          |    1 +
 7 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/drivers/char/vt.c b/drivers/char/vt.c
index e6a7916..2ef21da 100644
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -786,13 +786,15 @@ int vc_allocate(unsigned int currcons)	/
 	return 0;
 }
 
-static inline int resize_screen(struct vc_data *vc, int width, int height)
+static inline int resize_screen(struct vc_data *vc, int width, int height,
+				int user)
 {
 	/* Resizes the resolution of the display adapater */
 	int err = 0;
 
 	if (vc->vc_mode != KD_GRAPHICS && vc->vc_sw->con_resize)
-		err = vc->vc_sw->con_resize(vc, width, height);
+		err = vc->vc_sw->con_resize(vc, width, height, user);
+
 	return err;
 }
 
@@ -808,7 +810,7 @@ int vc_resize(struct vc_data *vc, unsign
 	unsigned long old_origin, new_origin, new_scr_end, rlth, rrem, err = 0;
 	unsigned int old_cols, old_rows, old_row_size, old_screen_size;
 	unsigned int new_cols, new_rows, new_row_size, new_screen_size;
-	unsigned int end;
+	unsigned int end, user;
 	unsigned short *newscreen;
 
 	WARN_CONSOLE_UNLOCKED();
@@ -816,6 +818,9 @@ int vc_resize(struct vc_data *vc, unsign
 	if (!vc)
 		return -ENXIO;
 
+	user = vc->vc_resize_user;
+	vc->vc_resize_user = 0;
+
 	if (cols > VC_RESIZE_MAXCOL || lines > VC_RESIZE_MAXROW)
 		return -EINVAL;
 
@@ -836,7 +841,7 @@ int vc_resize(struct vc_data *vc, unsign
 	old_row_size = vc->vc_size_row;
 	old_screen_size = vc->vc_screenbuf_size;
 
-	err = resize_screen(vc, new_cols, new_rows);
+	err = resize_screen(vc, new_cols, new_rows, user);
 	if (err) {
 		kfree(newscreen);
 		return err;
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index c872774..830e0ac 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -889,14 +889,24 @@ #endif
 	case VT_RESIZE:
 	{
 		struct vt_sizes __user *vtsizes = up;
+		struct vc_data *vc;
+
 		ushort ll,cc;
 		if (!perm)
 			return -EPERM;
 		if (get_user(ll, &vtsizes->v_rows) ||
 		    get_user(cc, &vtsizes->v_cols))
 			return -EFAULT;
-		for (i = 0; i < MAX_NR_CONSOLES; i++)
-			vc_lock_resize(vc_cons[i].d, cc, ll);
+
+		for (i = 0; i < MAX_NR_CONSOLES; i++) {
+			vc = vc_cons[i].d;
+
+			if (vc) {
+				vc->vc_resize_user = 1;
+				vc_lock_resize(vc_cons[i].d, cc, ll);
+			}
+		}
+
 		return 0;
 	}
 
@@ -942,6 +952,7 @@ #endif
 				vc_cons[i].d->vc_scan_lines = vlin;
 			if (clin)
 				vc_cons[i].d->vc_font.height = clin;
+			vc_cons[i].d->vc_resize_user = 1;
 			vc_resize(vc_cons[i].d, cc, ll);
 			release_console_sem();
 		}
diff --git a/drivers/usb/misc/sisusbvga/sisusb_con.c b/drivers/usb/misc/sisusbvga/sisusb_con.c
index 43722e5..b624320 100644
--- a/drivers/usb/misc/sisusbvga/sisusb_con.c
+++ b/drivers/usb/misc/sisusbvga/sisusb_con.c
@@ -1042,7 +1042,8 @@ sisusbcon_set_origin(struct vc_data *c)
 
 /* Interface routine */
 static int
-sisusbcon_resize(struct vc_data *c, unsigned int newcols, unsigned int newrows)
+sisusbcon_resize(struct vc_data *c, unsigned int newcols, unsigned int newrows,
+		 unsigned int user)
 {
 	struct sisusb_usb_data *sisusb;
 	int fh;
diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 6d0dcde..97a0224 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -2168,7 +2168,7 @@ static __inline__ void updatescrollmode(
 }
 
 static int fbcon_resize(struct vc_data *vc, unsigned int width, 
-			unsigned int height)
+			unsigned int height, unsigned int user)
 {
 	struct fb_info *info = registered_fb[con2fb_map[vc->vc_num]];
 	struct fbcon_ops *ops = info->fbcon_par;
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index 904bb24..a569871 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -1278,13 +1278,14 @@ #define vgacon_font_get NULL
 #endif
 
 static int vgacon_resize(struct vc_data *c, unsigned int width,
-				unsigned int height)
+			 unsigned int height, unsigned int user)
 {
 	if (width % 2 || width > ORIG_VIDEO_COLS ||
 	    height > (ORIG_VIDEO_LINES * vga_default_font_height)/
 	    c->vc_font.height)
-		/* let svgatextmode tinker with video timings */
-		return 0;
+		/* let svgatextmode tinker with video timings and
+		   return success */
+		return (user) ? 0 : -EINVAL;
 
 	if (CON_IS_VISIBLE(c) && !vga_is_gfx) /* who knows */
 		vgacon_doresize(c, width, height);
diff --git a/include/linux/console.h b/include/linux/console.h
index 9236a3f..a5f88a6 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -45,7 +45,8 @@ struct consw {
 	int	(*con_font_get)(struct vc_data *, struct console_font *);
 	int	(*con_font_default)(struct vc_data *, struct console_font *, char *);
 	int	(*con_font_copy)(struct vc_data *, int);
-	int	(*con_resize)(struct vc_data *, unsigned int, unsigned int);
+	int     (*con_resize)(struct vc_data *, unsigned int, unsigned int,
+			       unsigned int);
 	int	(*con_set_palette)(struct vc_data *, unsigned char *);
 	int	(*con_scrolldelta)(struct vc_data *, int);
 	int	(*con_set_origin)(struct vc_data *);
diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
index dc77fed..d71f7c0 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 */


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