In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
nfsd: hold rcu across localio cmpxchg retry<\/p>\n
nfsd_file objects are freed via call_rcu (filecache.c:296), and
\nnfsd_file_slab is created without SLAB_TYPESAFE_BY_RCU
\n(KMEM_CACHE(nfsd_file, 0) at filecache.c:789), so the slab page
\nbacking a freed nfsd_file becomes freely reclaimable once the RCU
\ngrace period elapses.<\/p>\n
The again: retry block in nfsd_open_local_fh() loads a pointer with
\ncmpxchg and then calls nfsd_file_get(new) (which is
\nrefcount_inc_not_zero) without holding rcu_read_lock. The sole caller
\nnfs_open_local_fh() drops rcu_read_lock before invoking this helper,
\nso no outer reader-side critical section covers the load.<\/p>\n
CPU 0 (nfsd_open_local_fh) CPU 1 (nfsd_file_put_local)
\n —– —–
\n new = cmpxchg(pnf, NULL, …)
\n nf = xchg(pnf, NULL)
\n nfsd_file_put(nf)
\n last ref -> call_rcu()
\n \/* grace period elapses;
\n slab page recycled *\/
\n nfsd_file_get(new)
\n refcount_inc_not_zero(&new->nf_ref)
\n \/* operates on recycled memory *\/<\/p>\n
A non-zero word at the nf_ref offset of the recycled object makes the
\nrefcount bump appear to succeed, and the caller then dereferences
\nnew->nf_net and new->nf_file out of freed memory.<\/p>\n
Fix by taking rcu_read_lock() immediately before the cmpxchg and
\nreleasing it on all three exits of the if (new) block: the goto-again
\nretry, the lost-race cleanup path, and the install-succeeded path.
\nnfsd_file_put() and nfsd_net_put() stay outside the RCU section so
\nthey remain free to block.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
nfsd: hold rcu across localio cmpxchg retry<\/p>\n
nfsd_file objects are freed via call_rcu (filecache.c:296), and
\nnfsd_file_slab is crea<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-21592","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/21592","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=21592"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=21592"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=21592"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}