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