MEDIUM: capabilities: enable support for Linux capabilities
For a while there has been the constraint of having to run as root for
transparent proxying, and we're starting to see some cases where QUIC is
not running in socket-per-connection mode due to the missing capability
that would be needed to bind a privileged port. It's not realistic to
ask all QUIC users on port 443 to run as root, so instead let's provide
a basic support for capabilities at least on linux. The ones currently
supported are cap_net_raw, cap_net_admin and cap_net_bind_service. The
mechanism was made OS-specific with a dedicated file because it really
is. It can be easily refined later for other OSes if needed.
A new keyword "setcaps" is added to the global section, to enumerate the
capabilities that must be kept when switching from root to non-root. This
is ignored in other situations though. HAProxy has to be built with
USE_LINUX_CAP=1 for this to be supported, which is enabled by default
for linux-glibc, linux-glibc-legacy and linux-musl.
A good way to test this is to start haproxy with such a config:
global
uid 1000
setcap cap_net_bind_service
frontend test
mode http
timeout client 3s
bind quic4@:443 ssl crt rsa+dh2048.pem allow-0rtt
and run it under "sudo strace -e trace=bind,setuid", then connecting
there from an H3 client. The bind() syscall must succeed despite the
user id having been switched.
This commit is contained in:
Willy Tarreau
parent
4d5f7d94b9
commit
bd84387beb
13
Makefile
13
Makefile
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@ -28,6 +28,7 @@
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# USE_TPROXY : enable transparent proxy. Automatic.
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# USE_LINUX_TPROXY : enable full transparent proxy. Automatic.
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# USE_LINUX_SPLICE : enable kernel 2.6 splicing. Automatic.
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# USE_LINUX_CAP : enable Linux capabilities.
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# USE_LIBCRYPT : enable encrypted passwords using -lcrypt
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# USE_CRYPT_H : set it if your system requires including crypt.h
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# USE_GETADDRINFO : use getaddrinfo() to resolve IPv6 host names.
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@ -305,7 +306,7 @@ LDFLAGS = $(ARCH_FLAGS) -g
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# specific entries if present before them.
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use_opts = USE_EPOLL USE_KQUEUE USE_NETFILTER USE_POLL \
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USE_THREAD USE_PTHREAD_EMULATION USE_BACKTRACE \
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USE_TPROXY USE_LINUX_TPROXY \
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USE_TPROXY USE_LINUX_TPROXY USE_LINUX_CAP \
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USE_LINUX_SPLICE USE_LIBCRYPT USE_CRYPT_H USE_ENGINE \
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USE_GETADDRINFO USE_OPENSSL USE_OPENSSL_WOLFSSL USE_SSL USE_LUA \
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USE_ACCEPT4 USE_CLOSEFROM USE_ZLIB USE_SLZ USE_CPU_AFFINITY \
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@ -347,7 +348,7 @@ endif
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ifeq ($(TARGET),linux-glibc)
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set_target_defaults = $(call default_opts, \
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USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER \
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USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_LINUX_TPROXY \
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USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_LINUX_TPROXY USE_LINUX_CAP \
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USE_ACCEPT4 USE_LINUX_SPLICE USE_PRCTL USE_THREAD_DUMP USE_NS USE_TFO \
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USE_GETADDRINFO USE_BACKTRACE USE_SHM_OPEN)
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INSTALL = install -v
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@ -357,7 +358,7 @@ endif
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ifeq ($(TARGET),linux-glibc-legacy)
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set_target_defaults = $(call default_opts, \
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USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER \
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USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_LINUX_TPROXY \
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USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_LINUX_TPROXY USE_LINUX_CAP \
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USE_ACCEPT4 USE_LINUX_SPLICE USE_PRCTL USE_THREAD_DUMP USE_GETADDRINFO)
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INSTALL = install -v
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endif
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@ -366,7 +367,7 @@ endif
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ifeq ($(TARGET),linux-musl)
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set_target_defaults = $(call default_opts, \
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USE_POLL USE_TPROXY USE_LIBCRYPT USE_DL USE_RT USE_CRYPT_H USE_NETFILTER \
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USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_LINUX_TPROXY \
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USE_CPU_AFFINITY USE_THREAD USE_EPOLL USE_LINUX_TPROXY USE_LINUX_CAP \
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USE_ACCEPT4 USE_LINUX_SPLICE USE_PRCTL USE_THREAD_DUMP USE_NS USE_TFO \
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USE_GETADDRINFO USE_SHM_OPEN)
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INSTALL = install -v
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@ -813,6 +814,10 @@ ifneq ($(USE_NS),)
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OPTIONS_OBJS += src/namespace.o
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endif
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ifneq ($(USE_LINUX_CAP),)
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OPTIONS_OBJS += src/linuxcap.o
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endif
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ifneq ($(USE_OT),)
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include addons/ot/Makefile
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endif
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@ -2183,6 +2183,22 @@ set-var-fmt <var-name> <fmt>
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set-var-fmt proc.current_state "primary"
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set-var-fmt proc.bootid "%pid|%t"
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setcap <name>[,<name>...]
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Sets a list of capabilities that must be preserved when starting with uid 0
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and switching to a non-zero uid. By default all permissions are lost by the
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uid switch, but some are often needed when trying connecting to a server from
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a foreign address during transparent proxying, or when binding to a port
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below 1024, e.g. when using "tune.quic.socket-owner connection", resulting in
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setups running entirely under uid 0. Setting capabilities generally is a
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safer alternative, as only the required capabilities will be preserved. The
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feature is OS-specific and only enabled on Linux when USE_LINUX_CAP=1 is set
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at build time. The list of supported capabilities also depends on the OS and
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is enumerated by the error message displayed when an invalid capability name
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or an empty one is passed. Multiple capabilities may be passed, delimited by
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commas. Among those commonly used, "cap_net_raw" allows to transparently bind
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to a foreign address, and "cap_net_bind_service" allows to bind to a
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privileged port and may be used by QUIC.
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setenv <name> <value>
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Sets environment variable <name> to value <value>. If the variable exists, it
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is overwritten. The changes immediately take effect so that the next line in
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@ -3424,7 +3440,8 @@ tune.quic.socket-owner { listener | connection }
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network stack. If your platform is deemed not compatible, haproxy will
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automatically switch to "listener" mode on startup. Please note that QUIC
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listeners running on privileged ports may require to run as uid 0, or some
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OS-specific tuning to permit the target uid to bind such ports.
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OS-specific tuning to permit the target uid to bind such ports, such as
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system capabilities. See also the "setcap" global directive.
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The "listener" value indicates that QUIC transfers will occur on the shared
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listener socket. This option can be a good compromise for small traffic as it
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@ -11645,7 +11662,8 @@ source <addr>[:<port>] [interface <name>]
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is possible at the server level using the "source" server option. Refer to
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section 5 for more information.
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In order to work, "usesrc" requires root privileges.
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In order to work, "usesrc" requires root privileges, or on supported systems,
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the "cap_net_raw" capability. See also the "setcap" global directive.
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Examples :
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backend private
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@ -0,0 +1,7 @@
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#ifndef _HAPROXY_LINUXCAP_H
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#define _HAPROXY_LINUXCAP_H
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int prepare_caps_for_setuid(int from_uid, int to_uid);
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int finalize_caps_after_setuid(int from_uid, int to_uid);
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#endif /* _HAPROXY_LINUXCAP_H */
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@ -108,6 +108,9 @@
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#include <haproxy/global.h>
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#include <haproxy/hlua.h>
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#include <haproxy/http_rules.h>
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#if defined(USE_LINUX_CAP)
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#include <haproxy/linuxcap.h>
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#endif
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#include <haproxy/list.h>
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#include <haproxy/listener.h>
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#include <haproxy/log.h>
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@ -3184,6 +3187,8 @@ static void *run_thread_poll_loop(void *data)
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/* set uid/gid depending on global settings */
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static void set_identity(const char *program_name)
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{
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int from_uid __maybe_unused = geteuid();
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if (global.gid) {
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if (getgroups(0, NULL) > 0 && setgroups(0, NULL) == -1)
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ha_warning("[%s.main()] Failed to drop supplementary groups. Using 'gid'/'group'"
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@ -3196,11 +3201,27 @@ static void set_identity(const char *program_name)
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}
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}
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#if defined(USE_LINUX_CAP)
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if (prepare_caps_for_setuid(from_uid, global.uid) < 0) {
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ha_alert("[%s.main()] Cannot switch uid to %d.\n", program_name, global.uid);
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protocol_unbind_all();
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exit(1);
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}
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#endif
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if (global.uid && setuid(global.uid) == -1) {
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ha_alert("[%s.main()] Cannot set uid %d.\n", program_name, global.uid);
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protocol_unbind_all();
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exit(1);
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}
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#if defined(USE_LINUX_CAP)
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if (finalize_caps_after_setuid(from_uid, global.uid) < 0) {
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ha_alert("[%s.main()] Cannot switch uid to %d.\n", program_name, global.uid);
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protocol_unbind_all();
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exit(1);
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}
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#endif
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}
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int main(int argc, char **argv)
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@ -0,0 +1,191 @@
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/*
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* Minimal handling of Linux kernel capabilities
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*
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* Copyright 2000-2023 Willy Tarreau <w@1wt.eu>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*
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*/
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/* Depending on distros, some have capset(), others use the more complicated
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* libcap. Let's stick to what we need and the kernel documents (capset).
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* Note that prctl is needed here.
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*/
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#include <linux/capability.h>
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#include <sys/prctl.h>
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#include <errno.h>
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#include <unistd.h>
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#include <syscall.h>
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#include <haproxy/api.h>
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#include <haproxy/cfgparse.h>
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#include <haproxy/errors.h>
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#include <haproxy/tools.h>
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/* supported names, zero-terminated */
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static const struct {
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int cap;
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const char *name;
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} known_caps[] = {
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#ifdef CAP_NET_RAW
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{ CAP_NET_RAW, "cap_net_raw" },
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#endif
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#ifdef CAP_NET_ADMIN
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{ CAP_NET_ADMIN, "cap_net_admin" },
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#endif
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#ifdef CAP_NET_BIND_SERVICE
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{ CAP_NET_BIND_SERVICE, "cap_net_bind_service" },
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#endif
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/* must be last */
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{ 0, 0 }
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};
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/* provided by sys/capability.h on some distros */
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static inline int capset(cap_user_header_t hdrp, const cap_user_data_t datap)
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{
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return syscall(SYS_capset, hdrp, datap);
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}
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/* defaults to zero, i.e. we don't keep any cap after setuid() */
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static uint32_t caplist;
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/* try to apply capabilities before switching UID from <from_uid> to <to_uid>.
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* In practice we need to do this in 4 steps:
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* - set PR_SET_KEEPCAPS to preserve caps across the final setuid()
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* - set the effective and permitted caps ;
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* - switch euid to non-zero
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* - set the effective and permitted caps again
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* - then the caller can safely call setuid()
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* We don't do this if the current euid is not zero or if the target uid
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* is zero. Returns >=0 on success, negative on failure. Alerts or warnings
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* may be emitted.
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*/
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int prepare_caps_for_setuid(int from_uid, int to_uid)
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{
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struct __user_cap_data_struct cap_data = { };
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struct __user_cap_header_struct cap_hdr = {
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.pid = 0, /* current process */
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.version = _LINUX_CAPABILITY_VERSION_1,
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};
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if (from_uid != 0)
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return 0;
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if (!to_uid)
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return 0;
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if (!caplist)
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return 0;
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if (prctl(PR_SET_KEEPCAPS, 1) == -1) {
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ha_alert("Failed to preserve capabilities using prctl(): %s\n", strerror(errno));
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return -1;
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}
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cap_data.effective = cap_data.permitted = caplist | (1 << CAP_SETUID);
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if (capset(&cap_hdr, &cap_data) == -1) {
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ha_alert("Failed to preset the capabilities to preserve using capset(): %s\n", strerror(errno));
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return -1;
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}
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if (seteuid(to_uid) == -1) {
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ha_alert("Failed to set effective uid to %d: %s\n", to_uid, strerror(errno));
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return -1;
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}
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cap_data.effective = cap_data.permitted = caplist | (1 << CAP_SETUID);
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if (capset(&cap_hdr, &cap_data) == -1) {
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ha_alert("Failed to set the final capabilities using capset(): %s\n", strerror(errno));
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return -1;
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}
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/* all's good */
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return 0;
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}
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/* finalize the capabilities after setuid(). The most important is to drop the
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* CAP_SET_SETUID capability, which would otherwise allow to switch back to any
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* UID and recover everything.
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*/
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int finalize_caps_after_setuid(int from_uid, int to_uid)
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{
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struct __user_cap_data_struct cap_data = { };
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struct __user_cap_header_struct cap_hdr = {
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.pid = 0, /* current process */
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.version = _LINUX_CAPABILITY_VERSION_1,
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};
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if (from_uid != 0)
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return 0;
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if (!to_uid)
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return 0;
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if (!caplist)
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return 0;
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cap_data.effective = cap_data.permitted = caplist;
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if (capset(&cap_hdr, &cap_data) == -1) {
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ha_alert("Failed to drop the setuid capability using capset(): %s\n", strerror(errno));
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return -1;
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}
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/* all's good */
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return 0;
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}
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/* parse the "setcap" global keyword. Returns -1 on failure, 0 on success. */
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static int cfg_parse_global_setcap(char **args, int section_type,
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struct proxy *curpx, const struct proxy *defpx,
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const char *file, int line, char **err)
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{
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char *name = args[1];
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char *next;
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uint32_t caps = 0;
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int id;
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if (!*name) {
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memprintf(err, "'%s' : missing capability name(s). ", args[0]);
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goto dump_caps;
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}
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while (name && *name) {
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next = strchr(name, ',');
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if (next)
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*(next++) = '\0';
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for (id = 0; known_caps[id].cap; id++) {
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if (strcmp(name, known_caps[id].name) == 0) {
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caps |= 1U << known_caps[id].cap;
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break;
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}
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}
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if (!known_caps[id].cap) {
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memprintf(err, "'%s' : unsupported capability '%s'. ", args[0], args[1]);
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goto dump_caps;
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}
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name = next;
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}
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caplist |= caps;
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return 0;
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dump_caps:
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memprintf(err, "%s Supported ones are: ", *err);
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for (id = 0; known_caps[id].cap; id++)
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memprintf(err, "%s%s%s%s", *err,
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id ? known_caps[id+1].cap ? ", " : " and " : "",
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known_caps[id].name, known_caps[id+1].cap ? "" : ".");
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return -1;
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}
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static struct cfg_kw_list cfg_kws = {ILH, {
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{ CFG_GLOBAL, "setcap", cfg_parse_global_setcap },
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{ 0, NULL, NULL }
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}};
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INITCALL1(STG_REGISTER, cfg_register_keywords, &cfg_kws);
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