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From 337d8d48b618d4fc0168a7b978be4c3447650b04 Mon Sep 17 00:00:00 2001
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From: Olivier Fourdan <ofourdan@redhat.com>
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Date: Fri, 5 Apr 2024 15:24:49 +0200
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Subject: [PATCH] render: Avoid possible double-free in ProcRenderAddGlyphs()
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ProcRenderAddGlyphs() adds the glyph to the glyphset using AddGlyph() and
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then frees it using FreeGlyph() to decrease the reference count, after
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AddGlyph() has increased it.
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AddGlyph() however may chose to reuse an existing glyph if it's already
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in the glyphSet, and free the glyph that was given, in which case the
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caller function, ProcRenderAddGlyphs() will call FreeGlyph() on an
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already freed glyph, as reported by ASan:
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READ of size 4 thread T0
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#0 in FreeGlyph xserver/render/glyph.c:252
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#1 in ProcRenderAddGlyphs xserver/render/render.c:1174
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#2 in Dispatch xserver/dix/dispatch.c:546
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#3 in dix_main xserver/dix/main.c:271
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#4 in main xserver/dix/stubmain.c:34
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#5 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
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#6 in __libc_start_main_impl ../csu/libc-start.c:360
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#7 (/usr/bin/Xwayland+0x44fe4)
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Address is located 0 bytes inside of 64-byte region
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freed by thread T0 here:
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#0 in __interceptor_free libsanitizer/asan/asan_malloc_linux.cpp:52
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#1 in _dixFreeObjectWithPrivates xserver/dix/privates.c:538
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#2 in AddGlyph xserver/render/glyph.c:295
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#3 in ProcRenderAddGlyphs xserver/render/render.c:1173
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#4 in Dispatch xserver/dix/dispatch.c:546
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#5 in dix_main xserver/dix/main.c:271
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#6 in main xserver/dix/stubmain.c:34
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#7 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
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previously allocated by thread T0 here:
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#0 in __interceptor_malloc libsanitizer/asan/asan_malloc_linux.cpp:69
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#1 in AllocateGlyph xserver/render/glyph.c:355
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#2 in ProcRenderAddGlyphs xserver/render/render.c:1085
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#3 in Dispatch xserver/dix/dispatch.c:546
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#4 in dix_main xserver/dix/main.c:271
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#5 in main xserver/dix/stubmain.c:34
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#6 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
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SUMMARY: AddressSanitizer: heap-use-after-free xserver/render/glyph.c:252 in FreeGlyph
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To avoid that, make sure not to free the given glyph in AddGlyph().
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v2: Simplify the test using the boolean returned from AddGlyph() (Michel)
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v3: Simplify even more by not freeing the glyph in AddGlyph() (Peter)
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Fixes: bdca6c3d1 - render: fix refcounting of glyphs during ProcRenderAddGlyphs
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Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1659
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Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
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Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1476>
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---
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render/glyph.c | 2 --
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1 file changed, 2 deletions(-)
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diff --git a/render/glyph.c b/render/glyph.c
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index 13991f8a1..5fa7f3b5b 100644
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--- a/render/glyph.c
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+++ b/render/glyph.c
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@@ -291,8 +291,6 @@ AddGlyph(GlyphSetPtr glyphSet, GlyphPtr glyph, Glyph id)
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gr = FindGlyphRef(&globalGlyphs[glyphSet->fdepth], signature,
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TRUE, glyph->sha1);
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if (gr->glyph && gr->glyph != DeletedGlyph && gr->glyph != glyph) {
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- FreeGlyphPicture(glyph);
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- dixFreeObjectWithPrivates(glyph, PRIVATE_GLYPH);
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glyph = gr->glyph;
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}
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else if (gr->glyph != glyph) {
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--
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2.44.0
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