CVE-2026-98361

In the Linux kernel, the following vulnerability has been resolved:

RDMA/rxe: Restore HMM PFN WRITE check in ODP write paths

Commit 0b261d7c1cd3 ("RDMA/rxe: Break endless pagefault loop for RO pages") dropped the access permission test from rxe check pagefault() and left only HMM PFN VALID. A page faulted in read-only, for example a page-cache folio behind a PROT READ file mapping, then satisfies the check and ODP write operations (RDMA WRITE, RDMA READ response, SEND payload, atomics) modify it through kmap without ever breaking CoW.

An unprivileged user can register an ODP MR over such a mapping and have incoming RDMA traffic overwrite the page cache of a file it only holds O RDONLY, including /etc/passwd or setuid binaries. This is the same primitive class as Dirty COW and CVE-2022-2590.

mlx5 has the missing invariant: its ODP path sets the device write bit only for pfns that carry HMM PFN WRITE. Restore it in rxe by requiring HMM PFN WRITE in rxe check pagefault() for every operation except RXE PAGEFAULT RDONLY. A write to a non-writable VMA now fails the one fault attempt with -EPERM from hmm vma fault() instead of re-faulting forever. For a writable VMA the fault breaks CoW and the write lands in the private page.

Keep pmem flushes on the read-only check. arch wb cache pmem() never modifies memory, and the FLUSH access bits do not make the umem writable, so classifying flushes as writes would make every flush against a flush-only MR fail.