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

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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: syzbot+29d4ed7f3bdedf2aa2fd@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=08b8be45afea11888776f897895aef9ad1c3ecfd
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/b34544687a1a09d6de630659eb7a773f4953238b.1600953813.git.yepeilin.cs@gmail.com
This commit is contained in:
Peilin Ye 2020-09-24 09:43:48 -04:00 committed by Daniel Vetter
parent 6735b4632d
commit 5af0864079
1 changed files with 12 additions and 0 deletions
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12
drivers/video/fbdev/core/fbcon.c
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@ -2471,6 +2471,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
if (font->width <= 8) {
j = vc->vc_font.height;
if (font->charcount * j > FNTSIZE(fontdata))
return -EINVAL;
for (i = 0; i < font->charcount; i++) {
memcpy(data, fontdata, j);
memset(data + j, 0, 32 - j);
@ -2479,6 +2482,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
}
} else if (font->width <= 16) {
j = vc->vc_font.height * 2;
if (font->charcount * j > FNTSIZE(fontdata))
return -EINVAL;
for (i = 0; i < font->charcount; i++) {
memcpy(data, fontdata, j);
memset(data + j, 0, 64 - j);
@ -2486,6 +2492,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
fontdata += j;
}
} 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 (j = 0; j < vc->vc_font.height; j++) {
*data++ = fontdata[0];
@ -2498,6 +2507,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
}
} else {
j = vc->vc_font.height * 4;
if (font->charcount * j > FNTSIZE(fontdata))
return -EINVAL;
for (i = 0; i < font->charcount; i++) {
memcpy(data, fontdata, j);
memset(data + j, 0, 128 - j);