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