GHSA-3v2r-c9x3-5fgr: 
In the Linux kernel, the following vulnerability has been resolved:sched/psi: fix race between file release and pressure writeA potential race condition exists between pressure write and cgroup file
release regarding the priv member of struct kernfs_open_file, which
triggers the uaf reported in [1].Consider the following scenario involving execution on two separate CPUs:CPU0					CPU1
   ====					====
					vfs_rmdir()
					kernfs_iop_rmdir()
					cgroup_rmdir()
					cgroup_kn_lock_live()
					cgroup_destroy_locked()
					cgroup_addrm_files()
					cgroup_rm_file()
					kernfs_remove_by_name()
					kernfs_remove_by_name_ns()
 vfs_write()				__kernfs_remove()
 new_sync_write()			kernfs_drain()
 kernfs_fop_write_iter()		kernfs_drain_open_files()
 cgroup_file_write()			kernfs_release_file()
 pressure_write()			cgroup_file_release()
 ctx = of->priv;
					kfree(ctx);
 					of->priv = NULL;
					cgroup_kn_unlock()
 cgroup_kn_lock_live()
 cgroup_get(cgrp)
 cgroup_kn_unlock()
 if (ctx->psi.trigger)  // here, trigger uaf for ctx, that is of->privThe cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards
the memory deallocation of of->priv performed within cgroup_file_release().
However, the operations involving of->priv executed within pressure_write()
are not entirely covered by the protection of cgroup_mutex. Consequently,
if the code in pressure_write(), specifically the section handling the
ctx variable executes after cgroup_file_release() has completed, a uaf
vulnerability involving of->priv is triggered.Therefore, the issue can be resolved by extending the scope of the
cgroup_mutex lock within pressure_write() to encompass all code paths
involving of->priv, thereby properly synchronizing the race condition
occurring between cgroup_file_release() and pressure_write().And, if an live kn lock can be successfully acquired while executing
the pressure write operation, it indicates that the cgroup deletion
process has not yet reached its final stage; consequently, the priv
pointer within open_file cannot be NULL. Therefore, the operation to
retrieve the ctx value must be moved to a point *after* the live kn
lock has been successfully acquired.In another situation, specifically after entering cgroup_kn_lock_live()
but before acquiring cgroup_mutex, there exists a different class of
race condition:CPU0: write memory.pressure               CPU1: write cgroup.pressure=0
===========================		  =============================kernfs_fop_write_iter()
 kernfs_get_active_of(of)
 pressure_write()
   cgroup_kn_lock_live(memory.pressure)
     cgroup_tryget(cgrp)
     kernfs_break_active_protection(kn)
     ... blocks on cgroup_mutex... acquires cgroup_mutex
   ctx = of->priv;        // may now be NULL
   if (ctx->psi.trigger)  // NULL dereferenceConsequently, there is a possibility that of->priv is NULL, the pressure
write needs to check for this.Now that the scope of the cgroup_mutex has been expanded, the original
explicit cgroup_get/put operations are no longer necessary, this is
because acquiring/releasing the live kn lock inherently executes a
cgroup get/put operation.[1]
BUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
Call Trace:
 pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
 cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:43
---truncated---
CVSS v3.1: 7.8