GHSA-FP98-H54J-VWFJ
Vulnerability from github – Published: 2026-09-16 12:30 – Updated: 2026-09-16 15:30In the Linux kernel, the following vulnerability has been resolved:
ublk: clear VM_MAYWRITE on read-only ublk char device mmap
ublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never clears VM_MAYWRITE on the resulting read-only mapping. This allows a userspace daemon to mmap the per-queue command buffer PROT_READ, then upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was never cleared.
The command buffer holds struct ublksrv_io_desc entries that are kernel-written ABI; a writable mapping lets an unprivileged daemon process corrupt fields such as addr, op_flags, nr_sectors, and start_sector.
Same bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and the 2026-08-13 ptp/vmclock fix (a5edadbae57e).
Verified via mprotect() PoC: before the fix, a PROT_READ mapping can be upgraded to PROT_READ|PROT_WRITE and a write into the command buffer corrupts io_desc fields (confirmed under KASAN). After the fix, mprotect() returns -EACCES.
{
"affected": [],
"aliases": [
"CVE-2026-89793"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T10:16:55Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nublk: clear VM_MAYWRITE on read-only ublk char device mmap\n\nublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never\nclears VM_MAYWRITE on the resulting read-only mapping. This allows\na userspace daemon to mmap the per-queue command buffer PROT_READ,\nthen upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was\nnever cleared.\n\nThe command buffer holds struct ublksrv_io_desc entries that are\nkernel-written ABI; a writable mapping lets an unprivileged daemon\nprocess corrupt fields such as addr, op_flags, nr_sectors, and\nstart_sector.\n\nSame bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and\nthe 2026-08-13 ptp/vmclock fix (a5edadbae57e).\n\nVerified via mprotect() PoC: before the fix, a PROT_READ mapping can\nbe upgraded to PROT_READ|PROT_WRITE and a write into the command\nbuffer corrupts io_desc fields (confirmed under KASAN). After the\nfix, mprotect() returns -EACCES.",
"id": "GHSA-fp98-h54j-vwfj",
"modified": "2026-09-16T15:30:57Z",
"published": "2026-09-16T12:30:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89793"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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