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Commit 43198a5b authored by Peilin Ye's avatar Peilin Ye Committed by Greg Kroah-Hartman
Browse files

fbcon: Fix global-out-of-bounds read in fbcon_get_font() 



commit 5af08640795b2b9a940c9266c0260455377ae262 upstream.

fbcon_get_font() is reading out-of-bounds. A malicious user may resize
`vc->vc_font.height` to a large value, causing fbcon_get_font() to
read out of `fontdata`.

fbcon_get_font() handles both built-in and user-provided fonts.
Fortunately, recently we have added FONT_EXTRA_WORDS support for built-in
fonts, so fix it by adding range checks using FNTSIZE().

This patch depends on patch "fbdev, newport_con: Move FONT_EXTRA_WORDS
macros into linux/font.h", and patch "Fonts: Support FONT_EXTRA_WORDS
macros for built-in fonts".

Cc: stable@vger.kernel.org
Reported-and-tested-by: default avatar <syzbot+29d4ed7f3bdedf2aa2fd@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?id=08b8be45afea11888776f897895aef9ad1c3ecfd


Signed-off-by: default avatarPeilin Ye <yepeilin.cs@gmail.com>
Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/b34544687a1a09d6de630659eb7a773f4953238b.1600953813.git.yepeilin.cs@gmail.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2162bcbc

drivers/video/fbdev/core/fbcon.c

+12 −0
Original line number Original line Diff line number Diff line
@@ -2270,6 +2270,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) 




	if (font->width <= 8) {

	if (font->width <= 8) {

		j = vc->vc_font.height;

		j = vc->vc_font.height;

		if (font->charcount * j > FNTSIZE(fontdata))

			return -EINVAL;



		for (i = 0; i < font->charcount; i++) {

		for (i = 0; i < font->charcount; i++) {

			memcpy(data, fontdata, j);

			memcpy(data, fontdata, j);

			memset(data + j, 0, 32 - j);

			memset(data + j, 0, 32 - j);
@@ -2278,6 +2281,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) 
		}

		}

	} else if (font->width <= 16) {

	} else if (font->width <= 16) {

		j = vc->vc_font.height * 2;

		j = vc->vc_font.height * 2;

		if (font->charcount * j > FNTSIZE(fontdata))

			return -EINVAL;



		for (i = 0; i < font->charcount; i++) {

		for (i = 0; i < font->charcount; i++) {

			memcpy(data, fontdata, j);

			memcpy(data, fontdata, j);

			memset(data + j, 0, 64 - j);

			memset(data + j, 0, 64 - j);
@@ -2285,6 +2291,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) 
			fontdata += j;

			fontdata += j;

		}

		}

	} else if (font->width <= 24) {

	} else if (font->width <= 24) {

		if (font->charcount * (vc->vc_font.height * sizeof(u32)) > FNTSIZE(fontdata))

			return -EINVAL;



		for (i = 0; i < font->charcount; i++) {

		for (i = 0; i < font->charcount; i++) {

			for (j = 0; j < vc->vc_font.height; j++) {

			for (j = 0; j < vc->vc_font.height; j++) {

				*data++ = fontdata[0];

				*data++ = fontdata[0];
@@ -2297,6 +2306,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) 
		}

		}

	} else {

	} else {

		j = vc->vc_font.height * 4;

		j = vc->vc_font.height * 4;

		if (font->charcount * j > FNTSIZE(fontdata))

			return -EINVAL;



		for (i = 0; i < font->charcount; i++) {

		for (i = 0; i < font->charcount; i++) {

			memcpy(data, fontdata, j);

			memcpy(data, fontdata, j);

			memset(data + j, 0, 128 - j);

			memset(data + j, 0, 128 - j);