CVE-2026-93243

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

mm/secretmem: properly account locked pages

secretmem accounts folios by treating memory as if it were mlock()'d and

thus limited by the RLIMIT_MEMLOCK limit.

However the folios are unevictable and remain so until the inode is

evicted, eliminating usual mlock() semantics - mapping folios then

unmapping them does not clear their unevictable state, since it depends on

AS_UNEVICTABLE, not PG_mlocked.

A user can therefore easily work around the RLIMIT_MEMLOCK limit - simply

map then unmap and VmLck no longer counts the secretmem range. Worse,

folios are not accounted in the process's RSS, meaning the OOM killer

won't know to kill the process.

Repeatedly mapping/unmapping (or forking) can then result in the

consumption of all available system memory with unevictable folios and

cause system instability.

A secretmem fd can be passed between processes and over fork so a

per-process limit simply does not make sense, so follow the precedent set

by io_uring, perf, skbuff, iommufd and xdp by tracking the number of

locked pages in user_struct->locked_vm.

Since the scope tracked is actually inode lifetime, the RLIMIT_MEMLOCK

applies per-user not per-process, so it doesn't make sense to bypass for

users with CAP_IPC_LOCK, therefore remove this bypass.

There is simply no reason to carry on marking the mapping as mlock()'d

since it's misleading and the lifecycle is now correctly handled, so

remove this too.

Note that secretmem does not support any form of truncation (including

hole punching) and the folios are unreclaimable, so the folios need only

be accounted on fault and unaccounted on inode destruction.

__secretmem_account_pages() is more or less a duplicate of the code that

io_uring etc. use, but since this is a bug fix that needs backporting,

defer any de-duplication efforts to a follow-up.

test_mlock_limit() asserts mlock_future_ok() on mmap(), however this has

been removed, so remove the test altogether for the fix. A new test will

be sent separately for upstream.