(release/25.1) glx: free old context tag before allocating new one in CommonMakeCurrent#3306
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oldTag in CommonMakeCurrent() is a pointer to cl->contextTags[...]. CommonMakeCurrent() may realloc(cl->contextTags) and thus move the memory, leaving oldTag as dangling pointer. If we then GlxFreeContextTag(oldTag) we end up writing into freed memory. Fix this by freeing oldTag before CommonMakeNewCurrent(). This vulnerability was discovered by: Anonymous working with Trend Micro Zero Day Initiative CVE-2026-56000/ZDI-CAN-30561 Fixes: 4781f2a ("GLX: Free the tag of the old context later") Assisted-by: Claude:claude-opus-4-6 Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2250> (cherry picked from commit 2779affbdb4354e894f490e56f962527d6125043) Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
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oldTag in CommonMakeCurrent() is a pointer to cl->contextTags[...].
CommonMakeCurrent() may realloc(cl->contextTags) and thus move the
memory, leaving oldTag as dangling pointer.
If we then GlxFreeContextTag(oldTag) we end up writing into freed
memory.
Fix this by freeing oldTag before CommonMakeNewCurrent().
This vulnerability was discovered by:
Anonymous working with Trend Micro Zero Day Initiative
CVE-2026-56000/ZDI-CAN-30561
Fixes: 4781f2a ("GLX: Free the tag of the old context later")
Assisted-by: Claude:claude-opus-4-6
Part-of: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2250
(cherry picked from commit 2779affbdb4354e894f490e56f962527d6125043)