1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
|
Description: Allow harmless group-writability
Allow secure files (~/.ssh/config, ~/.ssh/authorized_keys, etc.) to be
group-writable, provided that the group in question contains only the
file's owner. Rejected upstream for IMO incorrect reasons (e.g. a
misunderstanding about the contents of gr->gr_mem). Given that
per-user groups and umask 002 are the default setup in Debian (for good
reasons - this makes operating in setgid directories with other groups
much easier), we need to permit this by default.
Author: Colin Watson <cjwatson@debian.org>
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1060
Bug-Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=314347
Last-Update: 2010-02-27
Index: b/readconf.c
===================================================================
--- a/readconf.c
+++ b/readconf.c
@@ -30,6 +30,8 @@
#include <stdio.h>
#include <string.h>
#include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
#include "xmalloc.h"
#include "ssh.h"
@@ -1132,8 +1134,7 @@
if (fstat(fileno(f), &sb) == -1)
fatal("fstat %s: %s", filename, strerror(errno));
- if (((sb.st_uid != 0 && sb.st_uid != getuid()) ||
- (sb.st_mode & 022) != 0))
+ if (!secure_permissions(&sb, getuid()))
fatal("Bad owner or permissions on %s", filename);
}
Index: b/ssh.1
===================================================================
--- a/ssh.1
+++ b/ssh.1
@@ -1312,6 +1312,8 @@
.Xr ssh_config 5 .
Because of the potential for abuse, this file must have strict permissions:
read/write for the user, and not accessible by others.
+It may be group-writable provided that the group in question contains only
+the user.
.Pp
.It Pa ~/.ssh/environment
Contains additional definitions for environment variables; see
Index: b/ssh_config.5
===================================================================
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -1342,6 +1342,8 @@
This file is used by the SSH client.
Because of the potential for abuse, this file must have strict permissions:
read/write for the user, and not accessible by others.
+It may be group-writable provided that the group in question contains only
+the user.
.It Pa /etc/ssh/ssh_config
Systemwide configuration file.
This file provides defaults for those
Index: b/auth.c
===================================================================
--- a/auth.c
+++ b/auth.c
@@ -381,8 +381,7 @@
user_hostfile = tilde_expand_filename(userfile, pw->pw_uid);
if (options.strict_modes &&
(stat(user_hostfile, &st) == 0) &&
- ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
- (st.st_mode & 022) != 0)) {
+ !secure_permissions(&st, pw->pw_uid)) {
logit("Authentication refused for %.100s: "
"bad owner or modes for %.200s",
pw->pw_name, user_hostfile);
@@ -443,8 +442,7 @@
/* check the open file to avoid races */
if (fstat(fileno(f), &st) < 0 ||
- (st.st_uid != 0 && st.st_uid != uid) ||
- (st.st_mode & 022) != 0) {
+ !secure_permissions(&st, uid)) {
snprintf(err, errlen, "bad ownership or modes for file %s",
buf);
return -1;
@@ -459,8 +457,7 @@
strlcpy(buf, cp, sizeof(buf));
if (stat(buf, &st) < 0 ||
- (st.st_uid != 0 && st.st_uid != uid) ||
- (st.st_mode & 022) != 0) {
+ !secure_permissions(&st, uid)) {
snprintf(err, errlen,
"bad ownership or modes for directory %s", buf);
return -1;
Index: b/misc.c
===================================================================
--- a/misc.c
+++ b/misc.c
@@ -48,8 +48,9 @@
#include <netdb.h>
#ifdef HAVE_PATHS_H
# include <paths.h>
-#include <pwd.h>
#endif
+#include <pwd.h>
+#include <grp.h>
#ifdef SSH_TUN_OPENBSD
#include <net/if.h>
#endif
@@ -642,6 +643,55 @@
}
int
+secure_permissions(struct stat *st, uid_t uid)
+{
+ if (st->st_uid != 0 && st->st_uid != uid)
+ return 0;
+ if ((st->st_mode & 002) != 0)
+ return 0;
+ if ((st->st_mode & 020) != 0) {
+ /* If the file is group-writable, the group in question must
+ * have exactly one member, namely the file's owner.
+ * (Zero-member groups are typically used by setgid
+ * binaries, and are unlikely to be suitable.)
+ */
+ struct passwd *pw;
+ struct group *gr;
+ int members = 0;
+
+ gr = getgrgid(st->st_gid);
+ if (!gr)
+ return 0;
+
+ /* Check primary group memberships. */
+ while ((pw = getpwent()) != NULL) {
+ if (pw->pw_gid == gr->gr_gid) {
+ ++members;
+ if (pw->pw_uid != uid)
+ return 0;
+ }
+ }
+ endpwent();
+
+ pw = getpwuid(st->st_uid);
+ if (!pw)
+ return 0;
+
+ /* Check supplementary group memberships. */
+ if (gr->gr_mem[0]) {
+ ++members;
+ if (strcmp(pw->pw_name, gr->gr_mem[0]) ||
+ gr->gr_mem[1])
+ return 0;
+ }
+
+ if (!members)
+ return 0;
+ }
+ return 1;
+}
+
+int
tun_open(int tun, int mode)
{
#if defined(CUSTOM_SYS_TUN_OPEN)
Index: b/misc.h
===================================================================
--- a/misc.h
+++ b/misc.h
@@ -103,4 +103,6 @@
int ask_permission(const char *, ...) __attribute__((format(printf, 1, 2)));
int read_keyfile_line(FILE *, const char *, char *, size_t, u_long *);
+int secure_permissions(struct stat *st, uid_t uid);
+
#endif /* _MISC_H */
Index: b/auth-rhosts.c
===================================================================
--- a/auth-rhosts.c
+++ b/auth-rhosts.c
@@ -256,8 +256,7 @@
return 0;
}
if (options.strict_modes &&
- ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
- (st.st_mode & 022) != 0)) {
+ !secure_permissions(&st, pw->pw_uid)) {
logit("Rhosts authentication refused for %.100s: "
"bad ownership or modes for home directory.", pw->pw_name);
auth_debug_add("Rhosts authentication refused for %.100s: "
@@ -283,8 +282,7 @@
* allowing access to their account by anyone.
*/
if (options.strict_modes &&
- ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
- (st.st_mode & 022) != 0)) {
+ !secure_permissions(&st, pw->pw_uid)) {
logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
pw->pw_name, buf);
auth_debug_add("Bad file modes for %.200s", buf);
|
