Description
In the Linux kernel, the following vulnerability has been resolved:
virtio_ring: fix stale descriptor flags after a failed packed add
In a packed ring the AVAIL and USED bits sit in the descriptor itself,
so writing them makes that descriptor available. Those bit combinations
flip meaning on every round of the ring, tracked by a wrap counter, so
invalidating or validating a descriptor means inverting both bits.
Commit 1ce9e6055fa0 ("virtio_ring: introduce packed ring support") has
virtqueue_add_packed() make every descriptor of a chain available as it
maps the chain, and write the head last. The device consumes the ring in
order and stops at a head that is not available yet, so it never reaches
the rest.
When vring_map_one_sg() fails partway, unmap_release unmaps the segments
and restores avail_used_flags, but the descriptors it wrote to in the
ring stay marked with AVAIL and USED bits. The head is now the only
entry that keeps the device from consuming these stale entries.
For example, the ring would look like this now.
Z - pre-previous command
A - previous command
B - aborted command
C - current command
[A1 DONE] [A2 DONE] <C1 EMPTY> [B2] [B3] [Z1 DONE]
When the driver now attempts to issue the C command, the next add starts
at the same head as B. If C spans less descriptors than B, there is no
end marker because AVAIL and USED bits were still in place. And that
means the device will start interpreting these stale entries (B2/B3) as
another command entry, which then blocks the queue.
This effect typically happens in swiotlb configurations under memory
pressure, because vring_map_one_sg() can then fail with larger I/O
requests which then leads to command abortions.
There are broadly 2 ways to avoid leaving those flags behind:
1) Defer those flags too until the chain is complete.
2) Rewrite those flags for the previous wrap counter.
Implement the second option in both packed add paths. The first option
traverses the chain a second time on every successful add. The second
option invalidates all added descriptors when any add fails.
With this patch applied, a packed virtqueue keeps completing requests
after a failed add.
virtio_ring: fix stale descriptor flags after a failed packed add
In a packed ring the AVAIL and USED bits sit in the descriptor itself,
so writing them makes that descriptor available. Those bit combinations
flip meaning on every round of the ring, tracked by a wrap counter, so
invalidating or validating a descriptor means inverting both bits.
Commit 1ce9e6055fa0 ("virtio_ring: introduce packed ring support") has
virtqueue_add_packed() make every descriptor of a chain available as it
maps the chain, and write the head last. The device consumes the ring in
order and stops at a head that is not available yet, so it never reaches
the rest.
When vring_map_one_sg() fails partway, unmap_release unmaps the segments
and restores avail_used_flags, but the descriptors it wrote to in the
ring stay marked with AVAIL and USED bits. The head is now the only
entry that keeps the device from consuming these stale entries.
For example, the ring would look like this now.
Z - pre-previous command
A - previous command
B - aborted command
C - current command
[A1 DONE] [A2 DONE] <C1 EMPTY> [B2] [B3] [Z1 DONE]
When the driver now attempts to issue the C command, the next add starts
at the same head as B. If C spans less descriptors than B, there is no
end marker because AVAIL and USED bits were still in place. And that
means the device will start interpreting these stale entries (B2/B3) as
another command entry, which then blocks the queue.
This effect typically happens in swiotlb configurations under memory
pressure, because vring_map_one_sg() can then fail with larger I/O
requests which then leads to command abortions.
There are broadly 2 ways to avoid leaving those flags behind:
1) Defer those flags too until the chain is complete.
2) Rewrite those flags for the previous wrap counter.
Implement the second option in both packed add paths. The first option
traverses the chain a second time on every successful add. The second
option invalidates all added descriptors when any add fails.
With this patch applied, a packed virtqueue keeps completing requests
after a failed add.
Published:
2026-09-25
Score:
n/a
EPSS:
n/a
KEV:
No
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
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 | Linux | unaffected |
|
|||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
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References
History
Fri, 25 Sep 2026 10:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: virtio_ring: fix stale descriptor flags after a failed packed add In a packed ring the AVAIL and USED bits sit in the descriptor itself, so writing them makes that descriptor available. Those bit combinations flip meaning on every round of the ring, tracked by a wrap counter, so invalidating or validating a descriptor means inverting both bits. Commit 1ce9e6055fa0 ("virtio_ring: introduce packed ring support") has virtqueue_add_packed() make every descriptor of a chain available as it maps the chain, and write the head last. The device consumes the ring in order and stops at a head that is not available yet, so it never reaches the rest. When vring_map_one_sg() fails partway, unmap_release unmaps the segments and restores avail_used_flags, but the descriptors it wrote to in the ring stay marked with AVAIL and USED bits. The head is now the only entry that keeps the device from consuming these stale entries. For example, the ring would look like this now. Z - pre-previous command A - previous command B - aborted command C - current command [A1 DONE] [A2 DONE] <C1 EMPTY> [B2] [B3] [Z1 DONE] When the driver now attempts to issue the C command, the next add starts at the same head as B. If C spans less descriptors than B, there is no end marker because AVAIL and USED bits were still in place. And that means the device will start interpreting these stale entries (B2/B3) as another command entry, which then blocks the queue. This effect typically happens in swiotlb configurations under memory pressure, because vring_map_one_sg() can then fail with larger I/O requests which then leads to command abortions. There are broadly 2 ways to avoid leaving those flags behind: 1) Defer those flags too until the chain is complete. 2) Rewrite those flags for the previous wrap counter. Implement the second option in both packed add paths. The first option traverses the chain a second time on every successful add. The second option invalidates all added descriptors when any add fails. With this patch applied, a packed virtqueue keeps completing requests after a failed add. | |
| Title | virtio_ring: fix stale descriptor flags after a failed packed add | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-09-25T10:23:27.493Z
Reserved: 2026-09-25T10:18:58.209Z
Link: CVE-2026-97997
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-09-25T11:17:27.997
Modified: 2026-09-25T11:17:27.997
Link: CVE-2026-97997
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.