CVE-2026-90015

Description

In the Linux kernel, the following vulnerability has been resolved: xhci: fix lost bounce buffers on TDs spanning several ring segments When a TD reaches a link TRB with data that is not aligned to the endpoint's wMaxPacketSize, xhci_align_td() stages the unalignable tail through the bounce buffer of the ring segment holding that link TRB. xhci_unmap_td_bounce_buffer() later unmaps it and, for IN transfers, copies the data back into the URB's buffer. The enqueue path records the segment that was bounced in td->bounce_seg, under the assumption that a TD never spans more than two ring segments. That assumption does not hold: a TD large enough to span three or more segments crosses several link TRBs and can be bounced at each of them. Only the last one survives in td->bounce_seg, so every earlier bounce buffer is neither copied back nor DMA unmapped. The URB still completes with actual_length equal to the requested length and no error, so the transfer looks successful while a wMaxPacketSize sized hole in the destination buffer silently keeps its previous contents. It also leaks a DMA mapping per dropped bounce. Any sufficiently large and fragmented bulk transfer can hit this. It was found with a USB mass storage device behind xHCI backing a dm-verity target with 512 byte hash blocks, where the stale data is detected rather than silently consumed. The device enumerates as SuperSpeed, so wMaxPacketSize is 1024, while dm-bufio issues one 512 byte bio per hash block. verity_prefetch_io() makes the block layer merge hundreds of them into a single request of up to 512 scatterlist entries of 512 bytes each. At 256 TRBs per ring segment such a TD spans three segments, and every segment boundary falls on an odd multiple of 512, i.e. unaligned to wMaxPacketSize. dm-bufio then caches a hash block holding stale data and dm-verity declares the metadata block corrupted: device-mapper: verity: 8:2: metadata block 10850 is corrupted A reproducer running this under qemu is available at https://github.com/baloo/xhci-verity The bounce state (bounce_buf, bounce_dma, bounce_len, bounce_offs) already lives on the ring segment, so there is nothing extra to track. Keep recording the last bounced segment in td->bounce_seg and, on completion, walk the segments from td->start_seg up to it, unmapping every segment that still has a pending bounce. Stopping at td->bounce_seg rather than td->end_seg matters: a bounce implies the TD continues past that segment's link TRB, so bounce_seg is always strictly before end_seg, and a later TD may already have started in end_seg and been bounced there. Walking that far would copy a foreign bounce buffer into this URB and unmap it twice. It also keeps the walk correct if a TD ever wraps the whole ring so that end_seg == start_seg. [mn: Add ring->num_segs check to prevent unlikely infinite for loop.]

Gravité et risque d'exploitation

CVE-2026-90015 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.21 %, ce qui la place devant 10.6 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, <=6.12.*, <43239fc6dfb62c50ae1b9c0e82bac0f8cd2e285c, 5.15.221, 5.10.270, 0, 6.1.188, 6.18.51, <e04d5304a248e5d2a7f4faa87541644bdd320cfb, <ff44dfb03a293bf30e31f98772a1dd316a6071d1, <=5.10.*, <c8124b28f12dbdd126118e63d0ebf8093a01fb81, <=6.6.*, 7.2.5, 6.6.157, <a1629dfb011446d02905778f6df19f14c5f4f3b3, <=6.18.*, <efaab8938fb92979be6df359f7d1a43fb7e4717d, 6.12.110, <=7.2.*, 4.8, <=*, <=5.15.*, <7236bbd2cb7d9fc0eda896bbd34790341e2a4377, f9c589e142d04b8a19eb382162f804d17102b5ed, <4.8, <3c9a2b5a4f1183696f02ac280ced1d34afb409b1, 7.3) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/c8124b28f12dbdd126118e63d0ebf8093a01fb81
• https://git.kernel.org/stable/c/e04d5304a248e5d2a7f4faa87541644bdd320cfb
• https://git.kernel.org/stable/c/a1629dfb011446d02905778f6df19f14c5f4f3b3
• https://git.kernel.org/stable/c/43239fc6dfb62c50ae1b9c0e82bac0f8cd2e285c
• https://git.kernel.org/stable/c/3c9a2b5a4f1183696f02ac280ced1d34afb409b1
• https://git.kernel.org/stable/c/efaab8938fb92979be6df359f7d1a43fb7e4717d
• https://git.kernel.org/stable/c/7236bbd2cb7d9fc0eda896bbd34790341e2a4377
• https://git.kernel.org/stable/c/ff44dfb03a293bf30e31f98772a1dd316a6071d1