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List:       linux-stable-commits
Subject:    Patch "fbcon: Prevent that screen size is smaller than font size" has been added to the 4.19-stable 
From:       <gregkh () linuxfoundation ! org>
Date:       2022-07-31 12:16:26
Message-ID: 16592697861588 () kroah ! com
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This is a note to let you know that I've just added the patch titled

    fbcon: Prevent that screen size is smaller than font size

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fbcon-prevent-that-screen-size-is-smaller-than-font-size.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From foo@baz Sun Jul 31 01:15:34 PM CEST 2022
From: Chen Jun <chenjun102@huawei.com>
Date: Fri, 29 Jul 2022 03:11:39 +0000
Subject: fbcon: Prevent that screen size is smaller than font size
To: <stable@vger.kernel.org>, <deller@gmx.de>, <geert@linux-m68k.org>, \
                <b.zolnierkie@samsung.com>, <gregkh@linuxfoundation.org>
Cc: <xuqiang36@huawei.com>, <xiujianfeng@huawei.com>
Message-ID: <20220729031140.21806-2-chenjun102@huawei.com>

From: Helge Deller <deller@gmx.de>

commit e64242caef18b4a5840b0e7a9bff37abd4f4f933 upstream

We need to prevent that users configure a screen size which is smaller than the
currently selected font size. Otherwise rendering chars on the screen will
access memory outside the graphics memory region.

This patch adds a new function fbcon_modechange_possible() which
implements this check and which later may be extended with other checks
if necessary.  The new function is called from the FBIOPUT_VSCREENINFO
ioctl handler in fbmem.c, which will return -EINVAL if userspace asked
for a too small screen size.

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/all/20220706150253.2186-1-deller@gmx.de/
[sudip: adjust context]
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/video/fbdev/core/fbcon.c |   28 ++++++++++++++++++++++++++++
 drivers/video/fbdev/core/fbmem.c |   10 +++++++---
 include/linux/fbcon.h            |    4 ++++
 3 files changed, 39 insertions(+), 3 deletions(-)

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2729,6 +2729,34 @@ static void fbcon_set_all_vcs(struct fb_
 		fbcon_modechanged(info);
 }
 
+/* let fbcon check if it supports a new screen resolution */
+int fbcon_modechange_possible(struct fb_info *info, struct fb_var_screeninfo *var)
+{
+	struct fbcon_ops *ops = info->fbcon_par;
+	struct vc_data *vc;
+	unsigned int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
+	if (!ops)
+		return 0;
+
+	/* prevent setting a screen size which is smaller than font size */
+	for (i = first_fb_vc; i <= last_fb_vc; i++) {
+		vc = vc_cons[i].d;
+		if (!vc || vc->vc_mode != KD_TEXT ||
+			   registered_fb[con2fb_map[i]] != info)
+			continue;
+
+		if (vc->vc_font.width  > FBCON_SWAP(var->rotate, var->xres, var->yres) ||
+		    vc->vc_font.height > FBCON_SWAP(var->rotate, var->yres, var->xres))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fbcon_modechange_possible);
+
 static int fbcon_mode_deleted(struct fb_info *info,
 			      struct fb_videomode *mode)
 {
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1121,9 +1121,13 @@ static long do_fb_ioctl(struct fb_info *
 			console_unlock();
 			return -ENODEV;
 		}
-		info->flags |= FBINFO_MISC_USEREVENT;
-		ret = fb_set_var(info, &var);
-		info->flags &= ~FBINFO_MISC_USEREVENT;
+		ret = fbcon_modechange_possible(info, &var);
+		if (!ret) {
+			info->flags |= FBINFO_MISC_USEREVENT;
+			ret = fb_set_var(info, &var);
+			info->flags &= ~FBINFO_MISC_USEREVENT;
+		}
+		lock_fb_info(info);
 		unlock_fb_info(info);
 		console_unlock();
 		if (!ret && copy_to_user(argp, &var, sizeof(var)))
--- a/include/linux/fbcon.h
+++ b/include/linux/fbcon.h
@@ -4,9 +4,13 @@
 #ifdef CONFIG_FRAMEBUFFER_CONSOLE
 void __init fb_console_init(void);
 void __exit fb_console_exit(void);
+int  fbcon_modechange_possible(struct fb_info *info,
+			       struct fb_var_screeninfo *var);
 #else
 static inline void fb_console_init(void) {}
 static inline void fb_console_exit(void) {}
+static inline int  fbcon_modechange_possible(struct fb_info *info,
+				struct fb_var_screeninfo *var) { return 0; }
 #endif
 
 #endif /* _LINUX_FBCON_H */


Patches currently in stable-queue which might be from chenjun102@huawei.com are

queue-4.19/fbmem-check-virtual-screen-sizes-in-fb_set_var.patch
queue-4.19/fbcon-prevent-that-screen-size-is-smaller-than-font-size.patch


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