RE: [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers

On Thu, Sep 24, 2020 at 09:38:22AM -0400, Peilin Ye wrote:

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Hi all,

syzbot has reported [1] a global out-of-bounds read issue in fbcon_get_font(). A malicious user may resize `vc_font.height` to a large value in vt_ioctl(), causing fbcon_get_font() to overflow our built-in font data buffers, declared in lib/fonts/font_*.c:

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(drivers/video/fbdev/core/fbcon.c) if (font->width <= 8) { j = vc->vc_font.height;

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

• 	return -EINVAL;
  

Can that still go wrong because the multiply wraps?

David

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