CVE-2026-90015

xhci: fix lost bounce buffers on TDs spanning several ring segments

Published Sep 16, 2026 CVSS n/a EPSS < 1% KEV · Not listed

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.]

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< c8124b28f12dbdd126118e63d0ebf8093a01fb81
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< e04d5304a248e5d2a7f4faa87541644bdd320cfb
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< a1629dfb011446d02905778f6df19f14c5f4f3b3
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< 43239fc6dfb62c50ae1b9c0e82bac0f8cd2e285c
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< 3c9a2b5a4f1183696f02ac280ced1d34afb409b1
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< efaab8938fb92979be6df359f7d1a43fb7e4717d
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< 7236bbd2cb7d9fc0eda896bbd34790341e2a4377
`f9c589e142d04b8a19eb382162f804d17102b5ed`	affected	< ff44dfb03a293bf30e31f98772a1dd316a6071d1

Linux

affected

Version	Status	Constraints
`4.8`	affected	—
`0`	unaffected	< 4.8
`5.10.270`	unaffected	≤ 5.10.*
`5.15.221`	unaffected	≤ 5.15.*
`6.1.188`	unaffected	≤ 6.1.*
`6.6.157`	unaffected	≤ 6.6.*
`6.12.110`	unaffected	≤ 6.12.*
`6.18.51`	unaffected	≤ 6.18.*
`7.2.5`	unaffected	≤ 7.2.*
`7.3`	unaffected	≤ *

No data.

Vendor Product Versions

Linux

Linux Kernel

Version	Status	Scheme	Platform
`[f9c589e142d04b8a19eb382162f804d17102b5ed,c8124b28f12dbdd126118e63d0ebf8093a01fb81)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,e04d5304a248e5d2a7f4faa87541644bdd320cfb)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,a1629dfb011446d02905778f6df19f14c5f4f3b3)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,43239fc6dfb62c50ae1b9c0e82bac0f8cd2e285c)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,3c9a2b5a4f1183696f02ac280ced1d34afb409b1)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,efaab8938fb92979be6df359f7d1a43fb7e4717d)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,7236bbd2cb7d9fc0eda896bbd34790341e2a4377)`	affected	code_commit	—
`[f9c589e142d04b8a19eb382162f804d17102b5ed,ff44dfb03a293bf30e31f98772a1dd316a6071d1)`	affected	code_commit	—

Linux

Linux Kernel

Version	Status	Scheme	Platform
`4.8`	affected	generic	—
`[0,4.8)`	unaffected	generic	—
`[5.10.270,5.11.0)`	unaffected	semver	—
`[5.15.221,5.16.0)`	unaffected	semver	—
`[6.1.188,6.2.0)`	unaffected	semver	—
`[6.6.157,6.7.0)`	unaffected	semver	—
`[6.12.110,6.13.0)`	unaffected	semver	—
`[6.18.51,6.19.0)`	unaffected	semver	—
`[7.2.5,7.3.0)`	unaffected	semver	—
`[7.3-rc2,*]`	unaffected	generic	—

Remediation

No solution or workaround provided in the CVE record

Tracking

Advisories

Source	ID	Title
Debian DLA	DLA-4817-1	linux-6.12 security update
Debian DLA	DLA-4841-1	linux security update
Debian DSA	DSA-6528-1	linux security update
Ubuntu USN	USN-8961-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9019-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-9020-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9022-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9023-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9024-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9025-1	Linux kernel vulnerabilities
Ubuntu USN	USN-9026-1	Linux kernel (Azure) vulnerabilities
Ubuntu USN	USN-9029-1	Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN	USN-9039-1	Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN	USN-9040-1	Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN	USN-9066-1	Linux kernel (HWE) vulnerabilities
Ubuntu USN	USN-9091-1	Linux kernel (NVIDIA Tegra) vulnerabilities

Metrics

No CVSS v4.0

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.216% probability within 30 days)

Key SSVC decision points have not yet been added.

References

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

History

Sep 18, 2026 8:30 AM Weaknesses updated View changes

Type	Values Removed	Values Added
Weaknesses		CWE-200 CWE-401

Sep 16, 2026 10:45 AM Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references View changes

Type	Values Removed	Values Added
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.]
Title		xhci: fix lost bounce buffers on TDs spanning several ring segments
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/3c9a2b5a4f1183696f02ac280ced1d34afb409b1 https://git.kernel.org/stable/c/43239fc6dfb62c50ae1b9c0e82bac0f8cd2e285c https://git.kernel.org/stable/c/7236bbd2cb7d9fc0eda896bbd34790341e2a4377 https://git.kernel.org/stable/c/a1629dfb011446d02905778f6df19f14c5f4f3b3 https://git.kernel.org/stable/c/c8124b28f12dbdd126118e63d0ebf8093a01fb81 https://git.kernel.org/stable/c/e04d5304a248e5d2a7f4faa87541644bdd320cfb https://git.kernel.org/stable/c/efaab8938fb92979be6df359f7d1a43fb7e4717d https://git.kernel.org/stable/c/ff44dfb03a293bf30e31f98772a1dd316a6071d1