CVE-2026-89793

Summary

In 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 Software

VendorProductVersion RangeStatus
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < be41733c24be58e2a1ef718c80fafdfb98a40d5eaffected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5befd06a72216869b607cf7724a4f16c6a2d3999affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < e373c1acdbcf88cec533ece9f589020adaed0a78affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < fa5e1bc673ca59722608af67b27e65dba0c97926affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6e2b571b0a54755b06e092501913e1dfefe75d6caffected
LinuxLinux0 < 6.6.157affected
LinuxLinux0 < 6.12.110affected
LinuxLinux0 < 6.18.51affected
LinuxLinux0 < 7.2.5affected
LinuxLinux6.6.157 <= 6.6.*unaffected
LinuxLinux6.12.110 <= 6.12.*unaffected
LinuxLinux6.18.51 <= 6.18.*unaffected
LinuxLinux7.2.5 <= 7.2.*unaffected
LinuxLinux7.3-rc2 <= *unaffected

Weaknesses

References