# CVE-2026-64590: dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning

CVE-2026-64590 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-64590, released August 6, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-64590
- Priority: High
- CVSS: 7.1 (Important)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 6, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-64590

## Description

In the Linux kernel, the following vulnerability has been resolved:  dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning  When CONFIG_DMA_API_DEBUG_SG is enabled, importing a udmabuf into a DRM driver (e.g. amdgpu for video playback in GNOME Videos / Showtime) triggers a spurious warning:    DMA-API: amdgpu 0000:03:00.0: cacheline tracking EEXIST, \       overlapping mappings aren't supported   WARNING: kernel/dma/debug.c:619 at add_dma_entry+0x473/0x5f0  The call chain is:    amdgpu_cs_ioctl    -> amdgpu_ttm_backend_bind     -> dma_buf_map_attachment      -> [udmabuf] map_udmabuf -> get_sg_table       -> dma_map_sgtable(dev, sg, direction, 0)  // attrs=0        -> debug_dma_map_sg -> add_dma_entry -> EEXIST  This happens because udmabuf builds a per-page scatter-gather list via sg_set_folio().  When begin_cpu_udmabuf() has already created an sg table mapped for the misc device, and an importer such as amdgpu maps the same pages for its own device via map_udmabuf(), the DMA debug infrastructure sees two active mappings whose physical addresses share cacheline boundaries and warns about the overlap.  The DMA_ATTR_SKIP_CPU_SYNC flag suppresses this check in add_dma_entry() because it signals that no CPU cache maintenance is performed at map/unmap time, making the cacheline overlap harmless.  All other major dma-buf exporters already pass this flag:   - drm_gem_map_dma_buf() passes DMA_ATTR_SKIP_CPU_SYNC   - amdgpu_dma_buf_map() passes DMA_ATTR_SKIP_CPU_SYNC  The CPU sync at map/unmap time is also redundant for udmabuf: begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU access is requested through the dma-buf interface.  Pass DMA_ATTR_SKIP_CPU_SYNC to dma_map_sgtable() and dma_unmap_sgtable() in udmabuf to suppress the spurious warning and skip the redundant sync.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.187-1 | [DEBIAN-CVE-2026-64590](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64590.md) | Aug 6, 2026 |
| Linux | linux Debian 13.5 (trixie) | 6.12.96-1 | [DEBIAN-CVE-2026-64590](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64590.md) | Aug 6, 2026 |
| Linux | linux Debian 14 | 7.1.4-1 | [DEBIAN-CVE-2026-64590](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64590.md) | Aug 6, 2026 |
| Linux | linux-6.12 Debian 12.15 (bookworm) | 6.12.100-1~deb12u1 | [DEBIAN-CVE-2026-64590](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64590.md) | Aug 6, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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