virtio_ring: fix stale descriptor flags after a failed packed add

Summary

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.

Timeline

1. Sep 25, 2026, 10:23 AM UTCCVE published
2. Oct 21, 2026, 12:54 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 1ce9e6055fa0a9043405c5604cf19169ec5379ff · fixed in 5ad081761a1f0b0d95ab08b61a6008309fba95f9; From 1ce9e6055fa0a9043405c5604cf19169ec5379ff · fixed in cfe8128ceb78374b0f9cebb608bb48e3928d784a; From 1ce9e6055fa0a9043405c5604cf19169ec5379ff · fixed in 3e6400e3b8b858cdf0f8d70b20d8b55d703af368; From 1ce9e6055fa0a9043405c5604cf19169ec5379ff · fixed in d595358276b60e5df4d3930bc94033249b1d5adc; From 1ce9e6055fa0a9043405c5604cf19169ec5379ff · fixed in 75d276e5bb68778b2916f98a2bc30f142ebadc64

• Linux Linux

  5.0

• KernelLinux

  From 5.0.0 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.2.7

References 5