In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
exit: hold a reference to thread_pid across proc_flush_pid<\/p>\n
Commit 0a36bad01731 (“release_task: kill the no longer needed
\nget\/put_pid(thread_pid)”) removed the reference around proc_flush_pid().
\nIt assumed that free_pids(post.pids) at the end of release_task() would
\nkeep thread_pid alive until then.<\/p>\n
That assumption is wrong. __change_pid() only records a detached PID in
\npost.pids when pid_has_task() is false for every PIDTYPE. If another task
\nstill uses the exiting task’s PID as its process group or session ID,
\n__unhash_process() removes the exiting task’s PIDTYPE_PID link but leaves
\nthe PID out of post.pids. release_task() therefore holds no reference to
\nit after dropping tasklist_lock.<\/p>\n
The other task can then remove the remaining PIDTYPE links. Its
\nfree_pids() call schedules delayed_put_pid(), and the RCU callback can free
\nthe PID before the first release_task() reaches proc_flush_pid().<\/p>\n
An unprivileged reproducer races wait4(-1) against setsid() to trigger this
\nordering. Three of three fresh v7.2 KASAN boots reported:<\/p>\n
BUG: KASAN: slab-use-after-free in
\n proc_invalidate_siblings_dcache+0x3e2\/0x3f0
\n Read of size 8 by task h7_pid_reaper\/1921<\/p>\n
Call Trace:
\n proc_invalidate_siblings_dcache
\n release_task
\n wait_consider_task
\n __do_wait
\n do_wait
\n kernel_wait4<\/p>\n
Freed by task 0:
\n kmem_cache_free
\n put_pid
\n delayed_put_pid
\n rcu_core<\/p>\n
Last potentially related work creation:
\n __call_rcu_common
\n free_pids
\n ksys_setsid<\/p>\n
KASAN identified a 144-byte object from the pid cache and located the bad
\nread 80 bytes into the freed object, matching pid->inodes. With an
\nexplicit reference, three of three fresh boots completed without a KASAN
\nreport. The concurrent RCU callback dropped its reference while
\nproc_flush_pid() was protected, and the balancing put_pid() performed the
\nfinal free afterward.<\/p>\n
Take a reference before __unhash_process() clears p->thread_pid and release
\nit after proc_flush_pid() completes.<\/p>\n
A tested source reproducer is available privately on request. No
\ncontrolled read or write, information leak, or privilege escalation is
\nclaimed. The mainline patch applies directly to v6.19.y and newer;
\nv6.16.y through v6.18.y need a context-adjusted backport.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
exit: hold a reference to thread_pid across proc_flush_pid<\/p>\n
Commit 0a36bad01731 (“release_task: kill the no longer needed
\nget\/put_p<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-29059","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/29059","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=29059"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29059"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29059"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}