xref: /openbmc/linux/fs/notify/fanotify/fanotify.c (revision 5f32c314)
1 #include <linux/fanotify.h>
2 #include <linux/fdtable.h>
3 #include <linux/fsnotify_backend.h>
4 #include <linux/init.h>
5 #include <linux/jiffies.h>
6 #include <linux/kernel.h> /* UINT_MAX */
7 #include <linux/mount.h>
8 #include <linux/sched.h>
9 #include <linux/types.h>
10 #include <linux/wait.h>
11 
12 #include "fanotify.h"
13 
14 static bool should_merge(struct fsnotify_event *old_fsn,
15 			 struct fsnotify_event *new_fsn)
16 {
17 	struct fanotify_event_info *old, *new;
18 
19 	pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
20 	old = FANOTIFY_E(old_fsn);
21 	new = FANOTIFY_E(new_fsn);
22 
23 	if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
24 	    old->path.mnt == new->path.mnt &&
25 	    old->path.dentry == new->path.dentry)
26 		return true;
27 	return false;
28 }
29 
30 /* and the list better be locked by something too! */
31 static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
32 {
33 	struct fsnotify_event *test_event;
34 	bool do_merge = false;
35 
36 	pr_debug("%s: list=%p event=%p\n", __func__, list, event);
37 
38 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
39 	/*
40 	 * Don't merge a permission event with any other event so that we know
41 	 * the event structure we have created in fanotify_handle_event() is the
42 	 * one we should check for permission response.
43 	 */
44 	if (event->mask & FAN_ALL_PERM_EVENTS)
45 		return 0;
46 #endif
47 
48 	list_for_each_entry_reverse(test_event, list, list) {
49 		if (should_merge(test_event, event)) {
50 			do_merge = true;
51 			break;
52 		}
53 	}
54 
55 	if (!do_merge)
56 		return 0;
57 
58 	test_event->mask |= event->mask;
59 	return 1;
60 }
61 
62 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
63 static int fanotify_get_response_from_access(struct fsnotify_group *group,
64 					     struct fanotify_event_info *event)
65 {
66 	int ret;
67 
68 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
69 
70 	wait_event(group->fanotify_data.access_waitq, event->response ||
71 				atomic_read(&group->fanotify_data.bypass_perm));
72 
73 	if (!event->response) /* bypass_perm set */
74 		return 0;
75 
76 	/* userspace responded, convert to something usable */
77 	switch (event->response) {
78 	case FAN_ALLOW:
79 		ret = 0;
80 		break;
81 	case FAN_DENY:
82 	default:
83 		ret = -EPERM;
84 	}
85 	event->response = 0;
86 
87 	pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
88 		 group, event, ret);
89 
90 	return ret;
91 }
92 #endif
93 
94 static bool fanotify_should_send_event(struct fsnotify_mark *inode_mark,
95 				       struct fsnotify_mark *vfsmnt_mark,
96 				       u32 event_mask,
97 				       void *data, int data_type)
98 {
99 	__u32 marks_mask, marks_ignored_mask;
100 	struct path *path = data;
101 
102 	pr_debug("%s: inode_mark=%p vfsmnt_mark=%p mask=%x data=%p"
103 		 " data_type=%d\n", __func__, inode_mark, vfsmnt_mark,
104 		 event_mask, data, data_type);
105 
106 	/* if we don't have enough info to send an event to userspace say no */
107 	if (data_type != FSNOTIFY_EVENT_PATH)
108 		return false;
109 
110 	/* sorry, fanotify only gives a damn about files and dirs */
111 	if (!S_ISREG(path->dentry->d_inode->i_mode) &&
112 	    !S_ISDIR(path->dentry->d_inode->i_mode))
113 		return false;
114 
115 	if (inode_mark && vfsmnt_mark) {
116 		marks_mask = (vfsmnt_mark->mask | inode_mark->mask);
117 		marks_ignored_mask = (vfsmnt_mark->ignored_mask | inode_mark->ignored_mask);
118 	} else if (inode_mark) {
119 		/*
120 		 * if the event is for a child and this inode doesn't care about
121 		 * events on the child, don't send it!
122 		 */
123 		if ((event_mask & FS_EVENT_ON_CHILD) &&
124 		    !(inode_mark->mask & FS_EVENT_ON_CHILD))
125 			return false;
126 		marks_mask = inode_mark->mask;
127 		marks_ignored_mask = inode_mark->ignored_mask;
128 	} else if (vfsmnt_mark) {
129 		marks_mask = vfsmnt_mark->mask;
130 		marks_ignored_mask = vfsmnt_mark->ignored_mask;
131 	} else {
132 		BUG();
133 	}
134 
135 	if (S_ISDIR(path->dentry->d_inode->i_mode) &&
136 	    (marks_ignored_mask & FS_ISDIR))
137 		return false;
138 
139 	if (event_mask & marks_mask & ~marks_ignored_mask)
140 		return true;
141 
142 	return false;
143 }
144 
145 static int fanotify_handle_event(struct fsnotify_group *group,
146 				 struct inode *inode,
147 				 struct fsnotify_mark *inode_mark,
148 				 struct fsnotify_mark *fanotify_mark,
149 				 u32 mask, void *data, int data_type,
150 				 const unsigned char *file_name)
151 {
152 	int ret = 0;
153 	struct fanotify_event_info *event;
154 	struct fsnotify_event *fsn_event;
155 
156 	BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
157 	BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
158 	BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
159 	BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
160 	BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
161 	BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
162 	BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
163 	BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
164 	BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
165 	BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
166 
167 	if (!fanotify_should_send_event(inode_mark, fanotify_mark, mask, data,
168 					data_type))
169 		return 0;
170 
171 	pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
172 		 mask);
173 
174 	event = kmem_cache_alloc(fanotify_event_cachep, GFP_KERNEL);
175 	if (unlikely(!event))
176 		return -ENOMEM;
177 
178 	fsn_event = &event->fse;
179 	fsnotify_init_event(fsn_event, inode, mask);
180 	event->tgid = get_pid(task_tgid(current));
181 	if (data_type == FSNOTIFY_EVENT_PATH) {
182 		struct path *path = data;
183 		event->path = *path;
184 		path_get(&event->path);
185 	} else {
186 		event->path.mnt = NULL;
187 		event->path.dentry = NULL;
188 	}
189 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
190 	event->response = 0;
191 #endif
192 
193 	ret = fsnotify_add_notify_event(group, fsn_event, fanotify_merge);
194 	if (ret) {
195 		BUG_ON(mask & FAN_ALL_PERM_EVENTS);
196 		/* Our event wasn't used in the end. Free it. */
197 		fsnotify_destroy_event(group, fsn_event);
198 		ret = 0;
199 	}
200 
201 #ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
202 	if (mask & FAN_ALL_PERM_EVENTS) {
203 		ret = fanotify_get_response_from_access(group, event);
204 		fsnotify_destroy_event(group, fsn_event);
205 	}
206 #endif
207 	return ret;
208 }
209 
210 static void fanotify_free_group_priv(struct fsnotify_group *group)
211 {
212 	struct user_struct *user;
213 
214 	user = group->fanotify_data.user;
215 	atomic_dec(&user->fanotify_listeners);
216 	free_uid(user);
217 }
218 
219 static void fanotify_free_event(struct fsnotify_event *fsn_event)
220 {
221 	struct fanotify_event_info *event;
222 
223 	event = FANOTIFY_E(fsn_event);
224 	path_put(&event->path);
225 	put_pid(event->tgid);
226 	kmem_cache_free(fanotify_event_cachep, event);
227 }
228 
229 const struct fsnotify_ops fanotify_fsnotify_ops = {
230 	.handle_event = fanotify_handle_event,
231 	.free_group_priv = fanotify_free_group_priv,
232 	.free_event = fanotify_free_event,
233 };
234