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CVE-2026-74277
iommu/dma-iommu: Fix wrong scatterlist length assignment in P2PDMA path
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/iommu. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74277 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In iommu_dma_map_sg(), when handling PCI P2PDMA cases, the DMA length of the current scatterlist segment `s` is incorrectly assigned from the head entry `sg->length` instead of the current entry `s->length`. This typo causes all P2PDMA segments in the scatterlist to inherit the length of the first segment, leading to corrupted DMA lengths for multi- segment scatterlists. Fix this by using `s->length` instead of `sg->length`.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/iommu/dma-iommu.c
- What this is
- IOMMU DMA-API LAYERMAINTAINERS section matched on drivers/iommu/dma-iommu.c · iommu@lists.linux.dev · Maintained
Check it on the machine
grep -w CONFIG_IOMMU_DMA /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormYnot built on armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
- trixieYnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64
- forky, sidYnot built on armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_IOMMU_DMA
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/iommu
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.57 | 6166cb1344f1 |
| 6.16 | 7.1.5 | 8646f00ce021 |
| 6.16 | 7.2 | db50fb87015b |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- Exploitation requires local block/RDMA I/O that reaches dma_map_sg()/ib_dma_map_sg()→iommu_dma_map_sg() with multi-segment PCI P2PDMA scatterlists (e.g., NVMe-RDMA host, apple_nvme) on IOMMU-enabled systems; no direct remote packet handler invokes this mapping path.
- AC:LAttack complexity, low
- An attacker can reliably trigger the bug by crafting I/O sizes and alignments that yield multi-segment scatterlists with differing P2PDMA segment lengths; no uncontrollable heap layout, timing race, or rare victim state is required beyond P2PDMA-capable hardware topology.
- PR:LPrivileges required, low
- Any unprivileged local user with permission to perform I/O on a PCI device engaged in P2PDMA transfers (typical GPU/compute or storage device access) can trigger the corrupted mapping; real root in the init namespace is not required and user namespaces do not grant this capability.
- UI:NUser interaction, none
- No victim user action is needed beyond the attacker issuing their own read/write or RDMA/block I/O; exploitation does not depend on a separate user opening files, mounting filesystems, or clicking anything.
- S:CScope, changed
- Incorrect sg_dma_len values let PCIe DMA engines perform bus-address transfers beyond the intended buffer, bypassing IOMMU/DMA isolation and allowing a device’s DMA scope to affect host memory outside the mapped region.
- C:HConfidentiality impact, high
- When the first segment length exceeds a later P2PDMA segment’s true length, inflated DMA metadata causes the device to read past the buffer end over PCI, enabling disclosure of adjacent device or host memory comparable to an out-of-bounds DMA read.
- I:HIntegrity impact, high
- Corrupted DMA lengths permit out-of-bounds PCIe DMA writes beyond the allocated P2PDMA buffer, corrupting adjacent memory and providing a memory-corruption primitive that can be leveraged for further compromise of kernel-adjacent data.
- A:HAvailability impact, high
- Out-of-bounds DMA transfers can trigger IOMMU faults, device errors, and kernel oops/panics when hardware accesses unmapped or protected regions, and the corrupted mappings persist until unmap, enabling repeatable disruption.