Merge: CVE-2025-39881 kernel: kernfs: Fix UAF in polling when open file is released [rhel-9.8]

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7571

kernfs: Fix UAF in polling when open file is released

JIRA: https://issues.redhat.com/browse/RHEL-122088

Conflicts: Dropped llseek bits, as commit 0fedefd (kernfs: sysfs:
            support custom llseek method for sysfs entries) is not part of RHEL-9

CVE: CVE-2025-39881

Signed-off-by: Pavel Reichl <preichl@redhat.com>

Approved-by: Carlos Maiolino <cmaiolino@redhat.com>
Approved-by: Andrey Albershteyn <aalbersh@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

fs/kernfs/file.c

@@ -70,6 +70,24 @@ 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
  *
@@ -139,7 +157,7 @@ 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)
@@ -152,7 +170,7 @@ 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);
@@ -243,7 +261,7 @@ 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;
@@ -257,7 +275,7 @@ 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)
@@ -328,7 +346,7 @@ 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;
@@ -340,7 +358,7 @@ 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)
@@ -362,13 +380,13 @@ 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)
@@ -380,14 +398,14 @@ 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;
 }
 
@@ -400,7 +418,7 @@ 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;
@@ -409,7 +427,7 @@ 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;
 }
 
@@ -423,14 +441,14 @@ 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;
 }
 
@@ -460,7 +478,7 @@ 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);
@@ -493,7 +511,7 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
 	of->vm_ops = vma->vm_ops;
 	vma->vm_ops = &kernfs_vm_ops;
 out_put:
-	kernfs_put_active(of->kn);
+	kernfs_put_active_of(of);
 out_unlock:
 	mutex_unlock(&of->mutex);
 
@@ -847,15 +865,15 @@ 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)
 		ret = kn->attr.ops->poll(of, wait);
 	else
 		ret = kernfs_generic_poll(of, wait);
 
-	kernfs_put_active(kn);
+	kernfs_put_active_of(of);
 	return ret;
 }