1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * eCryptfs: Linux filesystem encryption layer
4  *
5  * Copyright (C) 2008 International Business Machines Corp.
6  *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
7  */
8 
9 #include <linux/kthread.h>
10 #include <linux/freezer.h>
11 #include <linux/slab.h>
12 #include <linux/wait.h>
13 #include <linux/mount.h>
14 #include "ecryptfs_kernel.h"
15 
16 struct ecryptfs_open_req {
17 	struct file **lower_file;
18 	struct path path;
19 	struct completion done;
20 	struct list_head kthread_ctl_list;
21 };
22 
23 static struct ecryptfs_kthread_ctl {
24 #define ECRYPTFS_KTHREAD_ZOMBIE 0x00000001
25 	u32 flags;
26 	struct mutex mux;
27 	struct list_head req_list;
28 	wait_queue_head_t wait;
29 } ecryptfs_kthread_ctl;
30 
31 static struct task_struct *ecryptfs_kthread;
32 
33 /**
34  * ecryptfs_threadfn
35  * @ignored: ignored
36  *
37  * The eCryptfs kernel thread that has the responsibility of getting
38  * the lower file with RW permissions.
39  *
40  * Returns zero on success; non-zero otherwise
41  */
ecryptfs_threadfn(void * ignored)42 static int ecryptfs_threadfn(void *ignored)
43 {
44 	set_freezable();
45 	while (1)  {
46 		struct ecryptfs_open_req *req;
47 
48 		wait_event_freezable(
49 			ecryptfs_kthread_ctl.wait,
50 			(!list_empty(&ecryptfs_kthread_ctl.req_list)
51 			 || kthread_should_stop()));
52 		mutex_lock(&ecryptfs_kthread_ctl.mux);
53 		if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
54 			mutex_unlock(&ecryptfs_kthread_ctl.mux);
55 			goto out;
56 		}
57 		while (!list_empty(&ecryptfs_kthread_ctl.req_list)) {
58 			req = list_first_entry(&ecryptfs_kthread_ctl.req_list,
59 					       struct ecryptfs_open_req,
60 					       kthread_ctl_list);
61 			list_del(&req->kthread_ctl_list);
62 			*req->lower_file = dentry_open(&req->path,
63 				(O_RDWR | O_LARGEFILE), current_cred());
64 			complete(&req->done);
65 		}
66 		mutex_unlock(&ecryptfs_kthread_ctl.mux);
67 	}
68 out:
69 	return 0;
70 }
71 
ecryptfs_init_kthread(void)72 int __init ecryptfs_init_kthread(void)
73 {
74 	int rc = 0;
75 
76 	mutex_init(&ecryptfs_kthread_ctl.mux);
77 	init_waitqueue_head(&ecryptfs_kthread_ctl.wait);
78 	INIT_LIST_HEAD(&ecryptfs_kthread_ctl.req_list);
79 	ecryptfs_kthread = kthread_run(&ecryptfs_threadfn, NULL,
80 				       "ecryptfs-kthread");
81 	if (IS_ERR(ecryptfs_kthread)) {
82 		rc = PTR_ERR(ecryptfs_kthread);
83 		printk(KERN_ERR "%s: Failed to create kernel thread; rc = [%d]"
84 		       "\n", __func__, rc);
85 	}
86 	return rc;
87 }
88 
ecryptfs_destroy_kthread(void)89 void ecryptfs_destroy_kthread(void)
90 {
91 	struct ecryptfs_open_req *req, *tmp;
92 
93 	mutex_lock(&ecryptfs_kthread_ctl.mux);
94 	ecryptfs_kthread_ctl.flags |= ECRYPTFS_KTHREAD_ZOMBIE;
95 	list_for_each_entry_safe(req, tmp, &ecryptfs_kthread_ctl.req_list,
96 				 kthread_ctl_list) {
97 		list_del(&req->kthread_ctl_list);
98 		*req->lower_file = ERR_PTR(-EIO);
99 		complete(&req->done);
100 	}
101 	mutex_unlock(&ecryptfs_kthread_ctl.mux);
102 	kthread_stop(ecryptfs_kthread);
103 	wake_up(&ecryptfs_kthread_ctl.wait);
104 }
105 
106 /**
107  * ecryptfs_privileged_open
108  * @lower_file: Result of dentry_open by root on lower dentry
109  * @lower_dentry: Lower dentry for file to open
110  * @lower_mnt: Lower vfsmount for file to open
111  * @cred: credential to use for this call
112  *
113  * This function gets a r/w file opened against the lower dentry.
114  *
115  * Returns zero on success; non-zero otherwise
116  */
ecryptfs_privileged_open(struct file ** lower_file,struct dentry * lower_dentry,struct vfsmount * lower_mnt,const struct cred * cred)117 int ecryptfs_privileged_open(struct file **lower_file,
118 			     struct dentry *lower_dentry,
119 			     struct vfsmount *lower_mnt,
120 			     const struct cred *cred)
121 {
122 	struct ecryptfs_open_req req;
123 	int flags = O_LARGEFILE;
124 	int rc = 0;
125 
126 	init_completion(&req.done);
127 	req.lower_file = lower_file;
128 	req.path.dentry = lower_dentry;
129 	req.path.mnt = lower_mnt;
130 
131 	/* Corresponding dput() and mntput() are done when the
132 	 * lower file is fput() when all eCryptfs files for the inode are
133 	 * released. */
134 	flags |= IS_RDONLY(d_inode(lower_dentry)) ? O_RDONLY : O_RDWR;
135 	(*lower_file) = dentry_open(&req.path, flags, cred);
136 	if (!IS_ERR(*lower_file))
137 		goto out;
138 	if ((flags & O_ACCMODE) == O_RDONLY) {
139 		rc = PTR_ERR((*lower_file));
140 		goto out;
141 	}
142 	mutex_lock(&ecryptfs_kthread_ctl.mux);
143 	if (ecryptfs_kthread_ctl.flags & ECRYPTFS_KTHREAD_ZOMBIE) {
144 		rc = -EIO;
145 		mutex_unlock(&ecryptfs_kthread_ctl.mux);
146 		printk(KERN_ERR "%s: We are in the middle of shutting down; "
147 		       "aborting privileged request to open lower file\n",
148 			__func__);
149 		goto out;
150 	}
151 	list_add_tail(&req.kthread_ctl_list, &ecryptfs_kthread_ctl.req_list);
152 	mutex_unlock(&ecryptfs_kthread_ctl.mux);
153 	wake_up(&ecryptfs_kthread_ctl.wait);
154 	wait_for_completion(&req.done);
155 	if (IS_ERR(*lower_file))
156 		rc = PTR_ERR(*lower_file);
157 out:
158 	return rc;
159 }
160