In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
nfsd: fix UAF in async copy cancel and shutdown<\/p>\n
An async copy could be freed or used after free while a teardown caller
\n(OFFLOAD_CANCEL, nfsd4_shutdown_copy, nfsd4_cancel_copy_by_sb) raced the
\ncopy kthread:<\/p>\n
– find_async_copy() bumped copy->refcount but left the copy on
\n clp->async_copies, so the reaper’s cleanup_async_copy() could run
\n release_copy_files() concurrently with a cancel\/shutdown caller. Both
\n put and NULL nf_src\/nf_dst without a common lock, double-putting the
\n nfsd_file and freeing it early.<\/p>\n
– nfsd4_do_async_copy() set NFSD4_COPY_F_STOPPED before its final uses
\n of the copy (nfsd_update_cmtime_attr() on copy->nf_dst,
\n nfsd4_send_cb_offload()). nfsd4_stop_copy() treats a set STOPPED bit
\n as “kthread done, skip kthread_stop()”, so a teardown caller ran
\n release_copy_files() — which puts and NULLs nf_dst — while the
\n kthread still dereferenced it (NULL\/UAF).<\/p>\n
– copy->copy_task was never pinned. The one-shot kthread self-reaps on
\n return, so kthread_stop()’s get_task_struct() could touch a freed
\n task_struct.<\/p>\n
– co_cb is embedded in the copy, but nfsd4_send_cb_offload() held a
\n reference only on the client, so a concurrent teardown could free
\n the copy while the CB_OFFLOAD callback was in flight.<\/p>\n
Fix the teardown lifetime as a whole:<\/p>\n
– find_async_copy() unlinks the copy (clear cp_clp, list_del_init)
\n under async_lock; the cancel, shutdown, and sb-cancel paths drop the
\n list-membership reference via nfs4_put_copy() after nfsd4_stop_copy().
\n Drop the now-redundant list_del fixup from cleanup_async_copy().<\/p>\n
– Because unlinking hides the copy from the reaper, its
\n cleanup_async_copy() can no longer remove the copy’s s2s_cp_stateids
\n entry; the cancel\/shutdown\/sb-cancel paths now call
\n nfs4_free_copy_state() themselves (while cp_clp is still valid) so
\n the entry does not dangle at freed memory for the laundromat and
\n manage_cpntf_state() to dereference.<\/p>\n
– Give the kthread its own reference, taken in nfsd4_copy() before
\n wake_up_process() and dropped at the end of nfsd4_do_async_copy();
\n call wake_up_process() before list_add().<\/p>\n
– Pin the task_struct with get_task_struct() in nfsd4_copy(), released
\n in nfs4_put_copy(), so kthread_stop() is safe whenever the kthread
\n exits. Set NFSD4_COPY_F_STOPPED only in nfsd4_stop_copy(), which now
\n always kthread_stop()s before release_copy_files(); completion is
\n still reported via NFSD4_COPY_F_COMPLETED, so
\n nfsd4_has_active_async_copies() is unaffected. Each teardown caller
\n removes the copy from clp->async_copies first, so kthread_stop() runs
\n exactly once.<\/p>\n
– Take a copy reference in nfsd4_send_cb_offload(), dropped in
\n nfsd4_cb_offload_release(). The kthread still holds its own reference
\n there, so the refcount_inc() cannot race the final free.<\/p>\n
– Read cp_clp with smp_load_acquire() to pair with the unordered
\n set_bit()\/clear_bit() writers (Documentation\/atomic_bitops.rst).<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
nfsd: fix UAF in async copy cancel and shutdown<\/p>\n
An async copy could be freed or used after free while a teardown caller
\n(OFFLOAD_C<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-21597","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/21597","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=21597"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=21597"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=21597"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}