[PATCH] tty: make FONTX ioctl use the tty pointer they were actually passed

[Tim Gardner]

From: Linus Torvalds <torvalds at linux-foundation.org>

BugLink: https://bugs.launchpad.net/bugs/1908150

commit 90bfdeef83f1d6c696039b6a917190dcbbad3220 upstream.

Some of the font tty ioctl's always used the current foreground VC for
their operations.  Don't do that then.

This fixes a data race on fg_console.

Side note: both Michael Ellerman and Jiri Slaby point out that all these
ioctls are deprecated, and should probably have been removed long ago,
and everything seems to be using the KDFONTOP ioctl instead.

In fact, Michael points out that it looks like busybox's loadfont
program seems to have switched over to using KDFONTOP exactly _because_
of this bug (ahem.. 12 years ago ;-).

Reported-by: Minh Yuan <yuanmingbuaa at gmail.com>
Acked-by: Michael Ellerman <mpe at ellerman.id.au>
Acked-by: Jiri Slaby <jirislaby at kernel.org>
Cc: Greg KH <greg at kroah.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
Signed-off-by: Ian May <ian.may at canonical.com>
(cherry picked from groovy/linux commit 161c231cb45fb23c5fbfcdd9d29cb72b6047ff61)
CVE-2020-25668
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 drivers/tty/vt/vt_ioctl.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
index e9ebe1520a56..142f3a5a01fc 100644
--- a/drivers/tty/vt/vt_ioctl.c
+++ b/drivers/tty/vt/vt_ioctl.c
@@ -244,7 +244,7 @@ int vt_waitactive(int n)
 
 
 static inline int 
-do_fontx_ioctl(int cmd, struct consolefontdesc __user *user_cfd, int perm, struct console_font_op *op)
+do_fontx_ioctl(struct vc_data *vc, int cmd, struct consolefontdesc __user *user_cfd, int perm, struct console_font_op *op)
 {
 	struct consolefontdesc cfdarg;
 	int i;
@@ -262,15 +262,16 @@ do_fontx_ioctl(int cmd, struct consolefontdesc __user *user_cfd, int perm, struc
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = cfdarg.chardata;
-		return con_font_op(vc_cons[fg_console].d, op);
-	case GIO_FONTX: {
+		return con_font_op(vc, op);
+
+	case GIO_FONTX:
 		op->op = KD_FONT_OP_GET;
 		op->flags = KD_FONT_FLAG_OLD;
 		op->width = 8;
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = cfdarg.chardata;
-		i = con_font_op(vc_cons[fg_console].d, op);
+		i = con_font_op(vc, op);
 		if (i)
 			return i;
 		cfdarg.charheight = op->height;
@@ -278,7 +279,6 @@ do_fontx_ioctl(int cmd, struct consolefontdesc __user *user_cfd, int perm, struc
 		if (copy_to_user(user_cfd, &cfdarg, sizeof(struct consolefontdesc)))
 			return -EFAULT;
 		return 0;
-		}
 	}
 	return -EINVAL;
 }
@@ -914,7 +914,7 @@ int vt_ioctl(struct tty_struct *tty,
 		op.height = 0;
 		op.charcount = 256;
 		op.data = up;
-		ret = con_font_op(vc_cons[fg_console].d, &op);
+		ret = con_font_op(vc, &op);
 		break;
 	}
 
@@ -925,7 +925,7 @@ int vt_ioctl(struct tty_struct *tty,
 		op.height = 32;
 		op.charcount = 256;
 		op.data = up;
-		ret = con_font_op(vc_cons[fg_console].d, &op);
+		ret = con_font_op(vc, &op);
 		break;
 	}
 
@@ -942,7 +942,7 @@ int vt_ioctl(struct tty_struct *tty,
 
 	case PIO_FONTX:
 	case GIO_FONTX:
-		ret = do_fontx_ioctl(cmd, up, perm, &op);
+		ret = do_fontx_ioctl(vc, cmd, up, perm, &op);
 		break;
 
 	case PIO_FONTRESET:
@@ -959,11 +959,11 @@ int vt_ioctl(struct tty_struct *tty,
 		{
 		op.op = KD_FONT_OP_SET_DEFAULT;
 		op.data = NULL;
-		ret = con_font_op(vc_cons[fg_console].d, &op);
+		ret = con_font_op(vc, &op);
 		if (ret)
 			break;
 		console_lock();
-		con_set_default_unimap(vc_cons[fg_console].d);
+		con_set_default_unimap(vc);
 		console_unlock();
 		break;
 		}
@@ -1090,8 +1090,9 @@ struct compat_consolefontdesc {
 };
 
 static inline int
-compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
-			 int perm, struct console_font_op *op)
+compat_fontx_ioctl(struct vc_data *vc, int cmd,
+		   struct compat_consolefontdesc __user *user_cfd,
+		   int perm, struct console_font_op *op)
 {
 	struct compat_consolefontdesc cfdarg;
 	int i;
@@ -1109,7 +1110,8 @@ compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = compat_ptr(cfdarg.chardata);
-		return con_font_op(vc_cons[fg_console].d, op);
+		return con_font_op(vc, op);
+
 	case GIO_FONTX:
 		op->op = KD_FONT_OP_GET;
 		op->flags = KD_FONT_FLAG_OLD;
@@ -1117,7 +1119,7 @@ compat_fontx_ioctl(int cmd, struct compat_consolefontdesc __user *user_cfd,
 		op->height = cfdarg.charheight;
 		op->charcount = cfdarg.charcount;
 		op->data = compat_ptr(cfdarg.chardata);
-		i = con_font_op(vc_cons[fg_console].d, op);
+		i = con_font_op(vc, op);
 		if (i)
 			return i;
 		cfdarg.charheight = op->height;
@@ -1207,7 +1209,7 @@ long vt_compat_ioctl(struct tty_struct *tty,
 	 */
 	case PIO_FONTX:
 	case GIO_FONTX:
-		return compat_fontx_ioctl(cmd, up, perm, &op);
+		return compat_fontx_ioctl(vc, cmd, up, perm, &op);
 
 	case KDFONTOP:
 		return compat_kdfontop_ioctl(up, perm, &op, vc);
-- 
2.17.1