Bug 2521420 (CVE-2026-74702)
| Summary: | CVE-2026-74702 kernel: vhost-scsi: reject feature changes after endpoint | ||
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| Product: | [Other] Security Response | Reporter: | OSIDB Bzimport <bzimport> |
| Component: | vulnerability | Assignee: | Product Security DevOps Team <prodsec-dev> |
| Status: | NEW --- | QA Contact: | |
| Severity: | medium | Docs Contact: | |
| Priority: | medium | ||
| Version: | unspecified | CC: | rhel-process-autobot, watson-tool-maintainers |
| Target Milestone: | --- | Keywords: | Security |
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | --- | |
| Doc Text: |
A flaw was found in the `vhost-scsi` component of the Linux kernel. This vulnerability allows a local attacker to cause a denial of service (DoS) by changing virtio feature bits after the `vhost-scsi` endpoint has been activated. Specifically, enabling the T10-PI feature after setup can lead to an inconsistent state where a null pointer is dereferenced during I/O operations, resulting in a kernel crash.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | Type: | --- | |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
In the Linux kernel, the following vulnerability has been resolved: vhost-scsi: reject feature changes after endpoint vhost_scsi_setup_vq_cmds() runs from VHOST_SCSI_SET_ENDPOINT and allocates each command's protection scatterlist array (prot_sgl) according to the acknowledged VIRTIO_SCSI_F_T10_PI bit. The command pools are not rebuilt when VHOST_SET_FEATURES changes that bit later. Although virtio feature bits must not change after feature negotiation, vhost_scsi_set_features() currently accepts such a request after the endpoint is active and updates acked_features. Enabling T10-PI after endpoint setup therefore leaves prot_sgl NULL while the I/O path follows the new feature bit. For a 129-page protection payload, vhost_scsi_mapal() passes the missing first chunk to sg_alloc_table_chained(): sg_alloc_table_chained(table, 129, first_chunk=NULL, nents_first_chunk=inline_sg_cnt) sg_pool_index() then hits: BUG_ON(nents > SG_CHUNK_SIZE); /* 129 > 128 */ The kernel reported the following call trace and register state: Call Trace: <TASK> ? __sg_alloc_table+0x1d8/0x250 ? __pfx_vhost_run_work_list+0x10/0x10 [vhost] sg_alloc_table_chained+0x59/0xf0 ? __pfx_sg_pool_alloc+0x10/0x10 ? vhost_scsi_calc_sgls.constprop.0+0x43/0x60 [vhost_scsi] vhost_scsi_handle_vq+0xf02/0x1700 [vhost_scsi] ? __pfx_vhost_scsi_handle_vq+0x10/0x10 [vhost_scsi] vhost_scsi_handle_kick+0x37/0x50 [vhost_scsi] vhost_run_work_list+0x8e/0xd0 [vhost] vhost_task_fn+0xe1/0x210 ret_from_fork+0x348/0x540 </TASK> RIP: 0010:0x4 CR2 = 0x4 RSP: 0018:ffffc90000dbf940 EFLAGS: 00010202 RAX: ffffffff82396810 RBX: ffff88811dc28b80 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000081 VHOST_F_LOG_ALL is a vhost-specific runtime feature and remains the only exception. Reject changes to any feature other than VHOST_F_LOG_ALL while the endpoint is active. This preserves the existing runtime log toggle while preventing feature-dependent command resources and data-path state from becoming inconsistent. Userspace must clear the endpoint before changing any other negotiated feature and set the endpoint up again afterward.