56 lines
2 KiB
Text
56 lines
2 KiB
Text
$NetBSD: patch-XSA-209-2,v 1.1 2017/03/20 18:09:21 bouyer Exp $
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From: Gerd Hoffmann <kraxel@redhat.com>
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Subject: [PATCH 3/3] cirrus: add blit_is_unsafe call to cirrus_bitblt_cputovideo
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CIRRUS_BLTMODE_MEMSYSSRC blits do NOT check blit destination
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and blit width, at all. Oops. Fix it.
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Security impact: high.
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The missing blit destination check allows to write to host memory.
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Basically same as CVE-2014-8106 for the other blit variants.
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The missing blit width check allows to overflow cirrus_bltbuf,
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with the attractive target cirrus_srcptr (current cirrus_bltbuf write
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position) being located right after cirrus_bltbuf in CirrusVGAState.
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Due to cirrus emulation writing cirrus_bltbuf bytewise the attacker
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hasn't full control over cirrus_srcptr though, only one byte can be
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changed. Once the first byte has been modified further writes land
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elsewhere.
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[ This is CVE-2017-2620 / XSA-209 - Ian Jackson ]
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Fixed compilation by removing extra parameter to blit_is_unsafe. -iwj
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Reported-by: Gerd Hoffmann <ghoffman@redhat.com>
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
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---
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diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
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index e6c3893..45facb6 100644
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--- qemu-xen-traditional/hw/cirrus_vga.c.orig
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+++ qemu-xen-traditional/hw/cirrus_vga.c
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@@ -900,6 +900,10 @@ static int cirrus_bitblt_cputovideo(CirrusVGAState * s)
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{
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int w;
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+ if (blit_is_unsafe(s)) {
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+ return 0;
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+ }
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+
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s->cirrus_blt_mode &= ~CIRRUS_BLTMODE_MEMSYSSRC;
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s->cirrus_srcptr = &s->cirrus_bltbuf[0];
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s->cirrus_srcptr_end = &s->cirrus_bltbuf[0];
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@@ -925,6 +929,10 @@ static int cirrus_bitblt_cputovideo(CirrusVGAState * s)
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}
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s->cirrus_srccounter = s->cirrus_blt_srcpitch * s->cirrus_blt_height;
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}
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+
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+ /* the blit_is_unsafe call above should catch this */
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+ assert(s->cirrus_blt_srcpitch <= CIRRUS_BLTBUFSIZE);
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+
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s->cirrus_srcptr = s->cirrus_bltbuf;
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s->cirrus_srcptr_end = s->cirrus_bltbuf + s->cirrus_blt_srcpitch;
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cirrus_update_memory_access(s);
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