linux-kernel - [PATCH v2 2/2] tty/vt: Avoid passing struct console_font_op to con_font

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Date:   Mon,  2 Nov 2020 04:37:55 -0500
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Thomas Winischhofer <thomas@...ischhofer.net>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Nicolas Pitre <nico@...xnic.net>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        George Kennedy <george.kennedy@...cle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Peter Rosin <peda@...ntia.se>, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, Peilin Ye <yepeilin.cs@...il.com>
Subject: [PATCH v2 2/2] tty/vt: Avoid passing struct console_font_op to con_font_copy()

con_font_op() is passing an entire `struct console_font_op *` to
con_font_copy(), but con_font_copy() only uses `op->height`. Additionally,
con_font_copy() is silently assigning the unsigned `op->height` to the
signed `con`, then pass it to fbcon_copy_font().

Let con_font_copy() and fbcon_copy_font() pass an unsigned int directly.
Also, add a comment in con_font_op() for less confusion, since ideally
`op->height` should not be used as a console index, as the field name
suggests.

This patch depends on patch "console: Remove dummy con_font_op() callback
implementations".

Suggested-by: Daniel Vetter <daniel@...ll.ch>
Signed-off-by: Peilin Ye <yepeilin.cs@...il.com>
---
con_font_set(), con_font_get() and con_font_default() also pass an entire
`console_font_op`.

con_font_get() and con_font_default() actually update the structure (later
copied to userspace), so let them be.

con_font_set() does not update the structure, but it uses all fields of it
except `op`. Avoiding passing `console_font_op` to con_font_set() will
thus make its signature pretty long (6 parameters).

Changes in v2:
  - Remove redundant `con < 0` check in con_font_copy() (kernel test robot
    <lkp@...el.com>)
  - Remove unnecessary range check in fbcon_copy_font(). con_font_copy()
    calls vc_cons_allocated(), which does the check
  - Do not Cc: stable
  - Rewrite the title and commit message accordingly

 drivers/tty/vt/vt.c              | 8 ++++----
 drivers/video/fbdev/core/fbcon.c | 2 +-
 include/linux/console.h          | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 9506a76f3ab6..27821ef97b13 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -4704,9 +4704,8 @@ static int con_font_default(struct vc_data *vc, struct console_font_op *op)
 	return rc;
 }
 
-static int con_font_copy(struct vc_data *vc, struct console_font_op *op)
+static int con_font_copy(struct vc_data *vc, unsigned int con)
 {
-	int con = op->height;
 	int rc;
 
 
@@ -4715,7 +4714,7 @@ static int con_font_copy(struct vc_data *vc, struct console_font_op *op)
 		rc = -EINVAL;
 	else if (!vc->vc_sw->con_font_copy)
 		rc = -ENOSYS;
-	else if (con < 0 || !vc_cons_allocated(con))
+	else if (!vc_cons_allocated(con))
 		rc = -ENOTTY;
 	else if (con == vc->vc_num)	/* nothing to do */
 		rc = 0;
@@ -4735,7 +4734,8 @@ int con_font_op(struct vc_data *vc, struct console_font_op *op)
 	case KD_FONT_OP_SET_DEFAULT:
 		return con_font_default(vc, op);
 	case KD_FONT_OP_COPY:
-		return con_font_copy(vc, op);
+		/* uses op->height as a console index */
+		return con_font_copy(vc, op->height);
 	}
 	return -ENOSYS;
 }
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index cef437817b0d..cb5b5705ea71 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2451,7 +2451,7 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h,
 	return 0;
 }
 
-static int fbcon_copy_font(struct vc_data *vc, int con)
+static int fbcon_copy_font(struct vc_data *vc, unsigned int con)
 {
 	struct fbcon_display *od = &fb_display[con];
 	struct console_font *f = &vc->vc_font;
diff --git a/include/linux/console.h b/include/linux/console.h
index 4b1e26c4cb42..34855d3f2afd 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -62,7 +62,7 @@ struct consw {
 	int	(*con_font_get)(struct vc_data *vc, struct console_font *font);
 	int	(*con_font_default)(struct vc_data *vc,
 			struct console_font *font, char *name);
-	int	(*con_font_copy)(struct vc_data *vc, int con);
+	int	(*con_font_copy)(struct vc_data *vc, unsigned int con);
 	int     (*con_resize)(struct vc_data *vc, unsigned int width,
 			unsigned int height, unsigned int user);
 	void	(*con_set_palette)(struct vc_data *vc,
-- 
2.25.1