Live › vulnerability › CVE-2026-99000
Go to dashboardThe Intel Xe graphics driver in the Linux kernel subtracts and adds shrinker page counts on every nested external pin and unpin, not only on the first pin and last unpin. Repeated pins of an external buffer, such as one with multiple dma-buf importers, can underflow those counts and make the memory shrinker run excessively under memory pressure.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Systems running a Linux kernel with the Intel Xe DRM driver (drm/xe) where external dma-buf objects can be pinned more than once, such as machines with multiple importers of the same buffer. The sources do not name affected kernel versions or say whether the flaw has a practical attack path beyond excessive shrinker activity.
No product ranges from the sources yet.
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In the Linux kernel, the following vulnerability has been resolved:
drm/xe: Fix shrinker accounting double-subtraction on nested external pins
xe_bo_pin_external() and xe_bo_unpin_external() support nested pins, since the underlying ttm_bo_pin()/ttm_bo_unpin() maintain a pin_count refcount rather than a boolean. However, the shrinker accounting calls xe_ttm_tt_account_subtract() and xe_ttm_tt_account_add() are invoked unconditionally on every pin_external()/unpin_external() call, instead of only on the transition into and out of the pinned state.
An external BO (dma-buf) can be pinned more than once while already pinned, for example when it has multiple attachments/importers, each independently calling xe_bo_pin_external(). Each such nested pin subtracts the BO's pages from the shrinker's accounting again, even though the BO's pages were already removed from consideration by the first pin. Symmetrically, each nested unpin adds them back again before the BO is actually unpinned. This desynchronizes the shrinker's page and object counts from reality, and since they are declared as signed long but interpreted as unsigned long in xe_shrinker_count(), the underflow can turn into an enormous shrinkable/purgeable page count, causing the shrinker to be invoked excessively under memory pressure.
Guard the accounting calls with the same pin-count transition checks already used to guard the pinned_link list maintenance, so accounting is only updated on the outermost pin and the final unpin.
While centralizing this logic into xe_bo_account_pin()/ xe_bo_account_unpin(), also close a second, related accounting gap affecting imported dma-bufs. For an imported bo's ttm_tt, xe's ttm_tt_populate hook (xe_ttm_tt_populate()) early-returns without calling xe_ttm_tt_account_add(), since TTM_TT_FLAG_EXTERNAL is set without TTM_TT_FLAG_EXTERNAL_MAPPABLE. However, TTM core's ttm_tt_populate() wrapper unconditionally marks the tt as populated on driver-hook success, so ttm_tt_is_populated() still reports true for it. xe_bo_account_pin()/xe_bo_account_unpin() trusted ttm_tt_is_populated() as a proxy for "these pages are accounted for by the shrinker", and would subtract/add pages for such a tt that were never added in the first place, again underflowing the shrinker's counts. This is reachable today via xe_bo_pin_external(), and would have become newly reachable via the fb-pin path once this patch routes __xe_pin_fb_vma() through xe_bo_pin_account() below, so fix it here rather than in a later patch, to avoid a commit in this series that introduces the regression before fixing it. Skip the accounting for imported bos, using the same EXTERNAL && !EXTERNAL_MAPPABLE test xe_ttm_tt_populate()/xe_ttm_tt_unpopulate() use to decide whether to act, via a new xe_ttm_bo_is_imported() helper (hoisted up from its only prior use site).
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