In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm\/secretmem: properly account locked pages<\/p>\n
secretmem accounts folios by treating memory as if it were mlock()’d and
\nthus limited by the RLIMIT_MEMLOCK limit.<\/p>\n
However the folios are unevictable and remain so until the inode is
\nevicted, eliminating usual mlock() semantics – mapping folios then
\nunmapping them does not clear their unevictable state, since it depends on
\nAS_UNEVICTABLE, not PG_mlocked.<\/p>\n
A user can therefore easily work around the RLIMIT_MEMLOCK limit – simply
\nmap then unmap and VmLck no longer counts the secretmem range. Worse,
\nfolios are not accounted in the process’s RSS, meaning the OOM killer
\nwon’t know to kill the process.<\/p>\n
Repeatedly mapping\/unmapping (or forking) can then result in the
\nconsumption of all available system memory with unevictable folios and
\ncause system instability.<\/p>\n
A secretmem fd can be passed between processes and over fork so a
\nper-process limit simply does not make sense, so follow the precedent set
\nby io_uring, perf, skbuff, iommufd and xdp by tracking the number of
\nlocked pages in user_struct->locked_vm.<\/p>\n
Since the scope tracked is actually inode lifetime, the RLIMIT_MEMLOCK
\napplies per-user not per-process, so it doesn’t make sense to bypass for
\nusers with CAP_IPC_LOCK, therefore remove this bypass.<\/p>\n
There is simply no reason to carry on marking the mapping as mlock()’d
\nsince it’s misleading and the lifecycle is now correctly handled, so
\nremove this too.<\/p>\n
Note that secretmem does not support any form of truncation (including
\nhole punching) and the folios are unreclaimable, so the folios need only
\nbe accounted on fault and unaccounted on inode destruction.<\/p>\n
__secretmem_account_pages() is more or less a duplicate of the code that
\nio_uring etc. use, but since this is a bug fix that needs backporting,
\ndefer any de-duplication efforts to a follow-up.<\/p>\n
test_mlock_limit() asserts mlock_future_ok() on mmap(), however this has
\nbeen removed, so remove the test altogether for the fix. A new test will
\nbe sent separately for upstream.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm\/secretmem: properly account locked pages<\/p>\n
secretmem accounts folios by treating memory as if it were mlock()’d and
\nthus limited <\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-28507","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/28507","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=28507"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=28507"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=28507"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}