1 /*
2  * Copyright (c) 2021 Omar Polo <op@openbsd.org>
3  *
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose with or without fee is hereby granted, provided that the above
6  * copyright notice and this permission notice appear in all copies.
7  *
8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15  */
16 
17 #include <linux/landlock.h>
18 
19 #include <sys/prctl.h>
20 #include <sys/syscall.h>
21 
22 #include <errno.h>
23 #include <unistd.h>
24 
25 #include "got_compat.h"
26 
27 /*
28  * What's the deal with landlock?  While distro with linux >= 5.13
29  * have the struct declarations, libc wrappers are missing.  The
30  * sample landlock code provided by the authors includes these "shims"
31  * in their example for the landlock API until libc provides them.
32  */
33 
34 #ifndef landlock_create_ruleset
35 static inline int
36 landlock_create_ruleset(const struct landlock_ruleset_attr *attr, size_t size,
37     __u32 flags)
38 {
39 	return syscall(__NR_landlock_create_ruleset, attr, size, flags);
40 }
41 #endif
42 
43 #ifndef landlock_add_rule
44 static inline int
45 landlock_add_rule(int ruleset_fd, enum landlock_rule_type type,
46     const void *attr, __u32 flags)
47 {
48 	return syscall(__NR_landlock_add_rule, ruleset_fd, type, attr, flags);
49 }
50 #endif
51 
52 #ifndef landlock_restrict_self
53 static inline int
54 landlock_restrict_self(int ruleset_fd, __u32 flags)
55 {
56 	return syscall(__NR_landlock_restrict_self, ruleset_fd, flags);
57 }
58 #endif
59 
60 /*
61  * Maybe we should ship with a full copy of the linux headers because
62  * you never know...
63  */
64 
65 #ifndef LANDLOCK_ACCESS_FS_REFER
66 #define LANDLOCK_ACCESS_FS_REFER	(1ULL << 13)
67 #endif
68 
69 #ifndef LANDLOCK_ACCESS_FS_TRUNCATE
70 #define LANDLOCK_ACCESS_FS_TRUNCATE	(1ULL << 14)
71 #endif
72 
73 /*
74  * Revoke any fs access.
75  */
76 int
77 landlock_no_fs(void)
78 {
79 	struct landlock_ruleset_attr rattr = {
80 		/* 
81 		 * List all capabilities currently defined by landlock.
82 		 * Failure in doing so will implicitly allow those actions
83 		 * (i.e. omitting READ_FILE will allow to read _any_ file.)
84 		 */
85 		.handled_access_fs =
86 		    LANDLOCK_ACCESS_FS_EXECUTE |
87 		    LANDLOCK_ACCESS_FS_READ_FILE |
88 		    LANDLOCK_ACCESS_FS_READ_DIR |
89 		    LANDLOCK_ACCESS_FS_WRITE_FILE |
90 		    LANDLOCK_ACCESS_FS_REMOVE_DIR |
91 		    LANDLOCK_ACCESS_FS_REMOVE_FILE |
92 		    LANDLOCK_ACCESS_FS_MAKE_CHAR |
93 		    LANDLOCK_ACCESS_FS_MAKE_DIR |
94 		    LANDLOCK_ACCESS_FS_MAKE_REG |
95 		    LANDLOCK_ACCESS_FS_MAKE_SOCK |
96 		    LANDLOCK_ACCESS_FS_MAKE_FIFO |
97 		    LANDLOCK_ACCESS_FS_MAKE_BLOCK |
98 		    LANDLOCK_ACCESS_FS_MAKE_SYM |
99 		    LANDLOCK_ACCESS_FS_REFER |
100 		    LANDLOCK_ACCESS_FS_TRUNCATE,
101 	};
102 	int fd, abi, saved_errno;
103 
104 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
105 		return -1;
106 
107 	abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
108 	if (abi == -1) {
109 		/* this kernel doesn't have landlock built in */
110 		if (errno == ENOSYS || errno == EOPNOTSUPP)
111 			return 0;
112 		return -1;
113 	}
114 	if (abi < 2)
115 		rattr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
116 	if (abi < 3)
117 		rattr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
118 
119 	fd = landlock_create_ruleset(&rattr, sizeof(rattr), 0);
120 	if (fd == -1)
121 		return -1;
122 
123 	if (landlock_restrict_self(fd, 0)) {
124 		saved_errno = errno;
125 		close(fd);
126 		errno = saved_errno;
127 		return -1;
128 	}
129 
130 	close(fd);
131 	return 0;
132 }