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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>
(cherry picked from commit bdca6c3d1f)
This commit is contained in:
Peter Hutterer 2024-01-30 13:13:35 +10:00 committed by Povilas Kanapickas
parent 0e34d8ebc9
commit 1173156404
3 changed files with 16 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
render/glyph.c
View File

@ -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);

2
render/glyphstr.h
View File

@ -109,6 +109,8 @@ 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);

15
render/render.c
View File

@ -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;