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tigervnc/SOURCES/xorg-CVE-2024-31083.patch

113 lines
3.6 KiB

From bdca6c3d1f5057eeb31609b1280fc93237b00c77 Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Tue, 30 Jan 2024 13:13:35 +1000
Subject: [PATCH 4/4] render: fix refcounting of glyphs during
ProcRenderAddGlyphs
Previously, AllocateGlyph would return a new glyph with refcount=0 and a
re-used glyph would end up not changing the refcount at all. The
resulting glyph_new array would thus have multiple entries pointing to
the same non-refcounted glyphs.
AddGlyph may free a glyph, resulting in a UAF when the same glyph
pointer is then later used.
Fix this by returning a refcount of 1 for a new glyph and always
incrementing the refcount for a re-used glyph, followed by dropping that
refcount back down again when we're done with it.
CVE-2024-31083, ZDI-CAN-22880
This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1463>
---
render/glyph.c | 5 +++--
render/glyphstr_priv.h | 1 +
render/render.c | 15 +++++++++++----
3 files changed, 15 insertions(+), 6 deletions(-)
diff --git a/render/glyph.c b/render/glyph.c
index 850ea8440..13991f8a1 100644
--- a/render/glyph.c
+++ b/render/glyph.c
@@ -245,10 +245,11 @@ FreeGlyphPicture(GlyphPtr glyph)
}
}
-static void
+void
FreeGlyph(GlyphPtr glyph, int format)
{
CheckDuplicates(&globalGlyphs[format], "FreeGlyph");
+ BUG_RETURN(glyph->refcnt == 0);
if (--glyph->refcnt == 0) {
GlyphRefPtr gr;
int i;
@@ -354,7 +355,7 @@ AllocateGlyph(xGlyphInfo * gi, int fdepth)
glyph = (GlyphPtr) malloc(size);
if (!glyph)
return 0;
- glyph->refcnt = 0;
+ glyph->refcnt = 1;
glyph->size = size + sizeof(xGlyphInfo);
glyph->info = *gi;
dixInitPrivates(glyph, (char *) glyph + head_size, PRIVATE_GLYPH);
diff --git a/render/glyphstr.h b/render/glyphstr.h
index 2f51bd244..3b1d806d1 100644
--- a/render/glyphstr.h
+++ b/render/glyphstr.h
@@ -108,6 +108,7 @@ extern Bool
extern GlyphPtr FindGlyph(GlyphSetPtr glyphSet, Glyph id);
extern GlyphPtr AllocateGlyph(xGlyphInfo * gi, int format);
+extern void FreeGlyph(GlyphPtr glyph, int format);
extern Bool
ResizeGlyphSet(GlyphSetPtr glyphSet, CARD32 change);
diff --git a/render/render.c b/render/render.c
index 29c5055c6..fe5e37dd9 100644
--- a/render/render.c
+++ b/render/render.c
@@ -1076,6 +1076,7 @@ ProcRenderAddGlyphs(ClientPtr client)
if (glyph_new->glyph && glyph_new->glyph != DeletedGlyph) {
glyph_new->found = TRUE;
+ ++glyph_new->glyph->refcnt;
}
else {
GlyphPtr glyph;
@@ -1168,8 +1169,10 @@ ProcRenderAddGlyphs(ClientPtr client)
err = BadAlloc;
goto bail;
}
- for (i = 0; i < nglyphs; i++)
+ for (i = 0; i < nglyphs; i++) {
AddGlyph(glyphSet, glyphs[i].glyph, glyphs[i].id);
+ FreeGlyph(glyphs[i].glyph, glyphSet->fdepth);
+ }
if (glyphsBase != glyphsLocal)
free(glyphsBase);
@@ -1179,9 +1182,13 @@ ProcRenderAddGlyphs(ClientPtr client)
FreePicture((void *) pSrc, 0);
if (pSrcPix)
FreeScratchPixmapHeader(pSrcPix);
- for (i = 0; i < nglyphs; i++)
- if (glyphs[i].glyph && !glyphs[i].found)
- free(glyphs[i].glyph);
+ for (i = 0; i < nglyphs; i++) {
+ if (glyphs[i].glyph) {
+ --glyphs[i].glyph->refcnt;
+ if (!glyphs[i].found)
+ free(glyphs[i].glyph);
+ }
+ }
if (glyphsBase != glyphsLocal)
free(glyphsBase);
return err;
--
2.44.0