fbcon: Fix global-out-of-bounds read in fbcon_get_font()
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
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@ -2471,6 +2471,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
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if (font->width <= 8) {
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j = vc->vc_font.height;
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if (font->charcount * j > FNTSIZE(fontdata))
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return -EINVAL;
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for (i = 0; i < font->charcount; i++) {
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memcpy(data, fontdata, j);
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memset(data + j, 0, 32 - j);
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@ -2479,6 +2482,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
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}
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} else if (font->width <= 16) {
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j = vc->vc_font.height * 2;
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if (font->charcount * j > FNTSIZE(fontdata))
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return -EINVAL;
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for (i = 0; i < font->charcount; i++) {
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memcpy(data, fontdata, j);
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memset(data + j, 0, 64 - j);
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@ -2486,6 +2492,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
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fontdata += j;
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}
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} else if (font->width <= 24) {
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if (font->charcount * (vc->vc_font.height * sizeof(u32)) > FNTSIZE(fontdata))
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return -EINVAL;
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for (i = 0; i < font->charcount; i++) {
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for (j = 0; j < vc->vc_font.height; j++) {
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*data++ = fontdata[0];
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@ -2498,6 +2507,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font)
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}
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} else {
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j = vc->vc_font.height * 4;
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if (font->charcount * j > FNTSIZE(fontdata))
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return -EINVAL;
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for (i = 0; i < font->charcount; i++) {
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memcpy(data, fontdata, j);
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memset(data + j, 0, 128 - j);
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