From: Chen Ridong <chenridong@huawei.com> stable inclusion from stable-v6.6.106 commit 854baafc00c433cccbe0ab4231b77aeb9b637b77 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/ICZCIL CVE: CVE-2025-39881 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=t... -------------------------------- commit 3c9ba2777d6c86025e1ba4186dc5cd930e40ec5f upstream. A use-after-free (UAF) vulnerability was identified in the PSI (Pressure Stall Information) monitoring mechanism: BUG: KASAN: slab-use-after-free in psi_trigger_poll+0x3c/0x140 Read of size 8 at addr ffff3de3d50bd308 by task systemd/1 psi_trigger_poll+0x3c/0x140 cgroup_pressure_poll+0x70/0xa0 cgroup_file_poll+0x8c/0x100 kernfs_fop_poll+0x11c/0x1c0 ep_item_poll.isra.0+0x188/0x2c0 Allocated by task 1: cgroup_file_open+0x88/0x388 kernfs_fop_open+0x73c/0xaf0 do_dentry_open+0x5fc/0x1200 vfs_open+0xa0/0x3f0 do_open+0x7e8/0xd08 path_openat+0x2fc/0x6b0 do_filp_open+0x174/0x368 Freed by task 8462: cgroup_file_release+0x130/0x1f8 kernfs_drain_open_files+0x17c/0x440 kernfs_drain+0x2dc/0x360 kernfs_show+0x1b8/0x288 cgroup_file_show+0x150/0x268 cgroup_pressure_write+0x1dc/0x340 cgroup_file_write+0x274/0x548 Reproduction Steps: 1. Open test/cpu.pressure and establish epoll monitoring 2. Disable monitoring: echo 0 > test/cgroup.pressure 3. Re-enable monitoring: echo 1 > test/cgroup.pressure The race condition occurs because: 1. When cgroup.pressure is disabled (echo 0 > cgroup.pressure), it: - Releases PSI triggers via cgroup_file_release() - Frees of->priv through kernfs_drain_open_files() 2. While epoll still holds reference to the file and continues polling 3. Re-enabling (echo 1 > cgroup.pressure) accesses freed of->priv epolling disable/enable cgroup.pressure fd=open(cpu.pressure) while(1) ... epoll_wait kernfs_fop_poll kernfs_get_active = true echo 0 > cgroup.pressure ... cgroup_file_show kernfs_show // inactive kn kernfs_drain_open_files cft->release(of); kfree(ctx); ... kernfs_get_active = false echo 1 > cgroup.pressure kernfs_show kernfs_activate_one(kn); kernfs_fop_poll kernfs_get_active = true cgroup_file_poll psi_trigger_poll // UAF ... end: close(fd) To address this issue, introduce kernfs_get_active_of() for kernfs open files to obtain active references. This function will fail if the open file has been released. Replace kernfs_get_active() with kernfs_get_active_of() to prevent further operations on released file descriptors. Fixes: 34f26a15611a ("sched/psi: Per-cgroup PSI accounting disable/re-enable interface") Cc: stable <stable@kernel.org> Reported-by: Zhang Zhaotian <zhangzhaotian@huawei.com> Signed-off-by: Chen Ridong <chenridong@huawei.com> Acked-by: Tejun Heo <tj@kernel.org> Link: https://lore.kernel.org/r/20250822070715.1565236-2-chenridong@huaweicloud.co... [ Drop llseek bits ] Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Long Li <leo.lilong@huawei.com> --- fs/kernfs/file.c | 54 ++++++++++++++++++++++++++++++++---------------- 1 file changed, 36 insertions(+), 18 deletions(-) diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index 9107151b6cfa..245b215cdda8 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -74,6 +74,24 @@ static struct kernfs_open_node *of_on(struct kernfs_open_file *of) !list_empty(&of->list)); } +/* Get active reference to kernfs node for an open file */ +static struct kernfs_open_file *kernfs_get_active_of(struct kernfs_open_file *of) +{ + /* Skip if file was already released */ + if (unlikely(of->released)) + return NULL; + + if (!kernfs_get_active(of->kn)) + return NULL; + + return of; +} + +static void kernfs_put_active_of(struct kernfs_open_file *of) +{ + return kernfs_put_active(of->kn); +} + /** * kernfs_deref_open_node_locked - Get kernfs_open_node corresponding to @kn * @@ -143,7 +161,7 @@ static void kernfs_seq_stop_active(struct seq_file *sf, void *v) if (ops->seq_stop) ops->seq_stop(sf, v); - kernfs_put_active(of->kn); + kernfs_put_active_of(of); } static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) @@ -156,7 +174,7 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) * the ops aren't called concurrently for the same open file. */ mutex_lock(&of->mutex); - if (!kernfs_get_active(of->kn)) + if (!kernfs_get_active_of(of)) return ERR_PTR(-ENODEV); ops = kernfs_ops(of->kn); @@ -242,7 +260,7 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) * the ops aren't called concurrently for the same open file. */ mutex_lock(&of->mutex); - if (!kernfs_get_active(of->kn)) { + if (!kernfs_get_active_of(of)) { len = -ENODEV; mutex_unlock(&of->mutex); goto out_free; @@ -256,7 +274,7 @@ static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) else len = -EINVAL; - kernfs_put_active(of->kn); + kernfs_put_active_of(of); mutex_unlock(&of->mutex); if (len < 0) @@ -327,7 +345,7 @@ static ssize_t kernfs_fop_write_iter(struct kiocb *iocb, struct iov_iter *iter) * the ops aren't called concurrently for the same open file. */ mutex_lock(&of->mutex); - if (!kernfs_get_active(of->kn)) { + if (!kernfs_get_active_of(of)) { mutex_unlock(&of->mutex); len = -ENODEV; goto out_free; @@ -339,7 +357,7 @@ static ssize_t kernfs_fop_write_iter(struct kiocb *iocb, struct iov_iter *iter) else len = -EINVAL; - kernfs_put_active(of->kn); + kernfs_put_active_of(of); mutex_unlock(&of->mutex); if (len > 0) @@ -361,13 +379,13 @@ static void kernfs_vma_open(struct vm_area_struct *vma) if (!of->vm_ops) return; - if (!kernfs_get_active(of->kn)) + if (!kernfs_get_active_of(of)) return; if (of->vm_ops->open) of->vm_ops->open(vma); - kernfs_put_active(of->kn); + kernfs_put_active_of(of); } static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf) @@ -379,14 +397,14 @@ static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf) if (!of->vm_ops) return VM_FAULT_SIGBUS; - if (!kernfs_get_active(of->kn)) + if (!kernfs_get_active_of(of)) return VM_FAULT_SIGBUS; ret = VM_FAULT_SIGBUS; if (of->vm_ops->fault) ret = of->vm_ops->fault(vmf); - kernfs_put_active(of->kn); + kernfs_put_active_of(of); return ret; } @@ -399,7 +417,7 @@ static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf) if (!of->vm_ops) return VM_FAULT_SIGBUS; - if (!kernfs_get_active(of->kn)) + if (!kernfs_get_active_of(of)) return VM_FAULT_SIGBUS; ret = 0; @@ -408,7 +426,7 @@ static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf) else file_update_time(file); - kernfs_put_active(of->kn); + kernfs_put_active_of(of); return ret; } @@ -422,14 +440,14 @@ static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr, if (!of->vm_ops) return -EINVAL; - if (!kernfs_get_active(of->kn)) + if (!kernfs_get_active_of(of)) return -EINVAL; ret = -EINVAL; if (of->vm_ops->access) ret = of->vm_ops->access(vma, addr, buf, len, write); - kernfs_put_active(of->kn); + kernfs_put_active_of(of); return ret; } @@ -459,7 +477,7 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma) mutex_lock(&of->mutex); rc = -ENODEV; - if (!kernfs_get_active(of->kn)) + if (!kernfs_get_active_of(of)) goto out_unlock; ops = kernfs_ops(of->kn); @@ -494,7 +512,7 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma) } vma->vm_ops = &kernfs_vm_ops; out_put: - kernfs_put_active(of->kn); + kernfs_put_active_of(of); out_unlock: mutex_unlock(&of->mutex); @@ -848,7 +866,7 @@ static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait) struct kernfs_node *kn = kernfs_dentry_node(filp->f_path.dentry); __poll_t ret; - if (!kernfs_get_active(kn)) + if (!kernfs_get_active_of(of)) return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI; if (kn->attr.ops->poll) @@ -856,7 +874,7 @@ static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait) else ret = kernfs_generic_poll(of, wait); - kernfs_put_active(kn); + kernfs_put_active_of(of); return ret; } -- 2.39.2