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
203
|
From 305ffb5ef0ba5ab1df32ef80f266a4c9e395ca13 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Sat, 16 Mar 2019 18:17:17 +0000
Subject: [PATCH 45/57] Improve kernel-capability manipulation code under
Linux.
Dnsmasq now fails early if a required capability is not available,
and tries not to request capabilities not required by its
configuration.
Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
---
CHANGELOG | 7 ++-
src/dnsmasq.c | 119 +++++++++++++++++++++++++++++++++-----------------
2 files changed, 84 insertions(+), 42 deletions(-)
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -28,7 +28,12 @@ version 2.81
Support TCP-fastopen (RFC-7413) on both incoming and
outgoing TCP connections, if supported and enabled in the OS.
-
+
+ Improve kernel-capability manipulation code under Linux. Dnsmasq
+ now fails early if a required capability is not available, and
+ tries not to request capabilities not required by its
+ configuration.
+
version 2.80
Add support for RFC 4039 DHCP rapid commit. Thanks to Ashram Method
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -52,6 +52,9 @@ int main (int argc, char **argv)
#if defined(HAVE_LINUX_NETWORK)
cap_user_header_t hdr = NULL;
cap_user_data_t data = NULL;
+ int need_cap_net_admin = 0;
+ int need_cap_net_raw = 0;
+ int need_cap_net_bind_service = 0;
char *bound_device = NULL;
int did_bind = 0;
#endif
@@ -285,11 +288,24 @@ int main (int argc, char **argv)
}
if (daemon->dhcp || daemon->relay4)
- dhcp_init();
+ {
+ dhcp_init();
+# ifdef HAVE_LINUX_NETWORK
+ if (!option_bool(OPT_NO_PING))
+ need_cap_net_raw = 1;
+ need_cap_net_admin = 1;
+# endif
+ }
# ifdef HAVE_DHCP6
if (daemon->doing_ra || daemon->doing_dhcp6 || daemon->relay6)
- ra_init(now);
+ {
+ ra_init(now);
+# ifdef HAVE_LINUX_NETWORK
+ need_cap_net_raw = 1;
+ need_cap_net_admin = 1;
+# endif
+ }
if (daemon->doing_dhcp6 || daemon->relay6)
dhcp6_init();
@@ -299,7 +315,12 @@ int main (int argc, char **argv)
#ifdef HAVE_IPSET
if (daemon->ipsets)
- ipset_init();
+ {
+ ipset_init();
+# ifdef HAVE_LINUX_NETWORK
+ need_cap_net_admin = 1;
+# endif
+ }
#endif
#if defined(HAVE_LINUX_NETWORK)
@@ -440,28 +461,58 @@ int main (int argc, char **argv)
}
#if defined(HAVE_LINUX_NETWORK)
+ /* We keep CAP_NETADMIN (for ARP-injection) and
+ CAP_NET_RAW (for icmp) if we're doing dhcp,
+ if we have yet to bind ports because of DAD,
+ or we're doing it dynamically,
+ we need CAP_NET_BIND_SERVICE. */
+ if ((is_dad_listeners() || option_bool(OPT_CLEVERBIND)) &&
+ (option_bool(OPT_TFTP) || (daemon->port != 0 && daemon->port <= 1024)))
+ need_cap_net_bind_service = 1;
+
/* determine capability API version here, while we can still
call safe_malloc */
- if (ent_pw && ent_pw->pw_uid != 0)
+ int capsize = 1; /* for header version 1 */
+ char *fail = NULL;
+
+ hdr = safe_malloc(sizeof(*hdr));
+
+ /* find version supported by kernel */
+ memset(hdr, 0, sizeof(*hdr));
+ capget(hdr, NULL);
+
+ if (hdr->version != LINUX_CAPABILITY_VERSION_1)
{
- int capsize = 1; /* for header version 1 */
- hdr = safe_malloc(sizeof(*hdr));
-
- /* find version supported by kernel */
- memset(hdr, 0, sizeof(*hdr));
- capget(hdr, NULL);
-
- if (hdr->version != LINUX_CAPABILITY_VERSION_1)
- {
- /* if unknown version, use largest supported version (3) */
- if (hdr->version != LINUX_CAPABILITY_VERSION_2)
- hdr->version = LINUX_CAPABILITY_VERSION_3;
- capsize = 2;
- }
-
- data = safe_malloc(sizeof(*data) * capsize);
- memset(data, 0, sizeof(*data) * capsize);
+ /* if unknown version, use largest supported version (3) */
+ if (hdr->version != LINUX_CAPABILITY_VERSION_2)
+ hdr->version = LINUX_CAPABILITY_VERSION_3;
+ capsize = 2;
}
+
+ data = safe_malloc(sizeof(*data) * capsize);
+ capget(hdr, data); /* Get current values, for verification */
+
+ if (need_cap_net_admin && !(data->permitted & (1 << CAP_NET_ADMIN)))
+ fail = "NET_ADMIN";
+ else if (need_cap_net_raw && !(data->permitted & (1 << CAP_NET_RAW)))
+ fail = "NET_RAW";
+ else if (need_cap_net_bind_service && !(data->permitted & (1 << CAP_NET_BIND_SERVICE)))
+ fail = "NET_BIND_SERVICE";
+
+ if (fail)
+ die(_("process is missing required capability %s"), fail, EC_MISC);
+
+ /* Now set bitmaps to set caps after daemonising */
+ memset(data, 0, sizeof(*data) * capsize);
+
+ if (need_cap_net_admin)
+ data->effective |= (1 << CAP_NET_ADMIN);
+ if (need_cap_net_raw)
+ data->effective |= (1 << CAP_NET_RAW);
+ if (need_cap_net_bind_service)
+ data->effective |= (1 << CAP_NET_BIND_SERVICE);
+
+ data->permitted = data->effective;
#endif
/* Use a pipe to carry signals and other events back to the event loop
@@ -626,18 +677,9 @@ int main (int argc, char **argv)
if (ent_pw && ent_pw->pw_uid != 0)
{
#if defined(HAVE_LINUX_NETWORK)
- /* On linux, we keep CAP_NETADMIN (for ARP-injection) and
- CAP_NET_RAW (for icmp) if we're doing dhcp. If we have yet to bind
- ports because of DAD, or we're doing it dynamically,
- we need CAP_NET_BIND_SERVICE too. */
- if (is_dad_listeners() || option_bool(OPT_CLEVERBIND))
- data->effective = data->permitted = data->inheritable =
- (1 << CAP_NET_ADMIN) | (1 << CAP_NET_RAW) |
- (1 << CAP_SETUID) | (1 << CAP_NET_BIND_SERVICE);
- else
- data->effective = data->permitted = data->inheritable =
- (1 << CAP_NET_ADMIN) | (1 << CAP_NET_RAW) | (1 << CAP_SETUID);
-
+ /* Need to be able to drop root. */
+ data->effective |= (1 << CAP_SETUID);
+ data->permitted |= (1 << CAP_SETUID);
/* Tell kernel to not clear capabilities when dropping root */
if (capset(hdr, data) == -1 || prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) == -1)
bad_capabilities = errno;
@@ -678,15 +720,10 @@ int main (int argc, char **argv)
}
#ifdef HAVE_LINUX_NETWORK
- if (is_dad_listeners() || option_bool(OPT_CLEVERBIND))
- data->effective = data->permitted =
- (1 << CAP_NET_ADMIN) | (1 << CAP_NET_RAW) | (1 << CAP_NET_BIND_SERVICE);
- else
- data->effective = data->permitted =
- (1 << CAP_NET_ADMIN) | (1 << CAP_NET_RAW);
- data->inheritable = 0;
+ data->effective &= ~(1 << CAP_SETUID);
+ data->permitted &= ~(1 << CAP_SETUID);
- /* lose the setuid and setgid capabilities */
+ /* lose the setuid capability */
if (capset(hdr, data) == -1)
{
send_event(err_pipe[1], EVENT_CAP_ERR, errno, NULL);
|
