--- filters/ip/nbdkit-ip-filter.pod | 63 ++++++++++++++++++++++++----- tests/Makefile.am | 14 ++++++- filters/ip/ip.c | 69 +++++++++++++++++++++++++++++--- tests/test-ip-filter-gid.sh | 51 ++++++++++++++++++++++++ tests/test-ip-filter-pid.sh | 70 +++++++++++++++++++++++++++++++++ tests/test-ip-filter-uid.sh | 51 ++++++++++++++++++++++++ 6 files changed, 300 insertions(+), 18 deletions(-) diff --git a/filters/ip/nbdkit-ip-filter.pod b/filters/ip/nbdkit-ip-filter.pod index 17108617..d7e0666b 100644 --- a/filters/ip/nbdkit-ip-filter.pod +++ b/filters/ip/nbdkit-ip-filter.pod @@ -1,6 +1,7 @@ =head1 NAME -nbdkit-ip-filter - filter clients by IP address +nbdkit-ip-filter - filter clients by IP address, process ID, user ID +or group ID =head1 SYNOPSIS @@ -14,6 +15,10 @@ address. Usually it is better to control this outside nbdkit, for example using TCP wrappers or a firewall, but this filter can be used if these are not available. +nbdkit E<ge> 1.24 added the ability to filter clients connecting over +local Unix domain sockets by client process ID, user ID and group ID. +This currently only works on Linux. + =head1 EXAMPLES nbdkit --filter=ip [...] allow=127.0.0.1,::1 deny=all @@ -28,13 +33,24 @@ network. nbdkit --filter=ip [...] allow=anyipv6 deny=all -Allow IPv6 clients to connect from anywhere, deny all IPv4 -connections. +Allow IPv6 clients to connect from anywhere, deny all other sources. + + nbdkit -U $tmpdir/sock --filter=ip [...] allow=uid:`id -u` deny=all + +Only allow the current user (S<C<id -u>>) to connect over the socket. +It is better to use this as an additional line of defense — also +create a temporary directory, make sure it is only accessible by the +user, and place the socket there. + + nbdkit -U sock --filter=ip [...] allow=gid:`id -g` deny=all + +Allow anyone in the same group as the current user to connect to the +Unix domain socket. =head1 RULES -When a client connects, this filter checks its IP address against the -allow and deny lists as follows: +When a client connects, this filter checks its source address against +the allow and deny lists as follows: =over 4 @@ -66,8 +82,7 @@ list of any of the following: =item B<any> -These keywords (which both have the same meaning) match any IP -address. +These keywords (which both have the same meaning) match any source. =item B<allipv4> @@ -100,6 +115,31 @@ address representations can be used (see S<RFC 5952>). This matches a range of IPv6 addresses C<A:B:.../NN>. +=item B<pid:>PID + +(nbdkit E<ge> 1.24, Linux only) + +This matches the process ID C<PID>, if the client connects over a Unix +domain socket. + +Note that process IDs are recycled so this alone is not secure enough +to ensure that only a single desired process can connect. However you +could add it as an additional check. + +=item B<uid:>UID + +(nbdkit E<ge> 1.24, Linux only) + +This matches the numeric user ID C<UID>, if the client connects over a +Unix domain socket. + +=item B<gid:>GID + +(nbdkit E<ge> 1.24, Linux only) + +This matches the numeric group ID C<GID>, if the client connects over +a Unix domain socket. + =back =head2 Not filtered @@ -107,8 +147,11 @@ This matches a range of IPv6 addresses C<A:B:.../NN>. If neither the C<allow> nor the C<deny> parameter is given the filter does nothing. -The filter permits non-IP connections, such as Unix domain sockets or -AF_VSOCK. +C<AF_VSOCK> connections are always unfiltered. + +Unix domain sockets were always unfiltered in S<nbdkit E<le> 1.22>. +In S<nbdkit E<ge> 1.24> it is possible to apply filtering to them on +Linux. =head1 PARAMETERS @@ -155,4 +198,4 @@ Richard W.M. Jones =head1 COPYRIGHT -Copyright (C) 2019 Red Hat Inc. +Copyright (C) 2019-2020 Red Hat Inc. diff --git a/tests/Makefile.am b/tests/Makefile.am index b5b06810..cacbbce9 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -1437,8 +1437,18 @@ test_gzip_CFLAGS = $(WARNINGS_CFLAGS) $(LIBGUESTFS_CFLAGS) test_gzip_LDADD = libtest.la $(LIBGUESTFS_LIBS) # ip filter test. -TESTS += test-ip-filter.sh -EXTRA_DIST += test-ip-filter.sh +TESTS += \ + test-ip-filter.sh \ + test-ip-filter-pid.sh \ + test-ip-filter-uid.sh \ + test-ip-filter-gid.sh \ + $(NULL) +EXTRA_DIST += \ + test-ip-filter.sh \ + test-ip-filter-pid.sh \ + test-ip-filter-uid.sh \ + test-ip-filter-gid.sh \ + $(NULL) # limit filter test. TESTS += test-limit.sh diff --git a/filters/ip/ip.c b/filters/ip/ip.c index b16ec55c..2f702c01 100644 --- a/filters/ip/ip.c +++ b/filters/ip/ip.c @@ -62,12 +62,13 @@ int ip_debug_rules; struct rule { struct rule *next; - enum { BAD = 0, ANY, ANYV4, ANYV6, IPV4, IPV6 } type; + enum { BAD = 0, ANY, ANYV4, ANYV6, IPV4, IPV6, PID, UID, GID } type; union { - struct in_addr ipv4; + struct in_addr ipv4; /* for IPV4, IPV6 */ struct in6_addr ipv6; + int64_t id; /* for PID, UID and GID */ } u; - unsigned prefixlen; + unsigned prefixlen; /* for IPV4, IPV6 */ }; static struct rule *allow_rules, *allow_rules_last; @@ -100,6 +101,16 @@ print_rule (const char *name, const struct rule *rule, const char *suffix) nbdkit_debug ("%s=ipv6:[%s]/%u%s", name, u.addr6, rule->prefixlen, suffix); break; + case PID: + nbdkit_debug ("%s=pid:%" PRIi64 "%s", name, rule->u.id, suffix); + break; + case UID: + nbdkit_debug ("%s=uid:%" PRIi64 "%s", name, rule->u.id, suffix); + break; + case GID: + nbdkit_debug ("%s=gid:%" PRIi64 "%s", name, rule->u.id, suffix); + break; + case BAD: nbdkit_debug ("%s=BAD(!)%s", name, suffix); break; @@ -227,6 +238,37 @@ parse_rule (const char *paramname, return 0; } + if (n >= 4 && ascii_strncasecmp (value, "pid:", 4) == 0) { + new_rule->type = PID; + if (nbdkit_parse_int64_t ("pid:", &value[4], &new_rule->u.id) == -1) + return -1; + if (new_rule->u.id <= 0) { + nbdkit_error ("pid: parameter out of range"); + return -1; + } + return 0; + } + if (n >= 4 && ascii_strncasecmp (value, "uid:", 4) == 0) { + new_rule->type = UID; + if (nbdkit_parse_int64_t ("uid:", &value[4], &new_rule->u.id) == -1) + return -1; + if (new_rule->u.id < 0) { + nbdkit_error ("uid: parameter out of range"); + return -1; + } + return 0; + } + if (n >= 4 && ascii_strncasecmp (value, "gid:", 4) == 0) { + new_rule->type = GID; + if (nbdkit_parse_int64_t ("gid:", &value[4], &new_rule->u.id) == -1) + return -1; + if (new_rule->u.id < 0) { + nbdkit_error ("gid: parameter out of range"); + return -1; + } + return 0; + } + /* Address with prefixlen. */ if ((p = strchr (value, '/')) != NULL) { size_t pllen = &value[n] - &p[1]; @@ -401,6 +443,19 @@ matches_rule (const struct rule *rule, sin6 = (struct sockaddr_in6 *) addr; return ipv6_equal (sin6->sin6_addr, rule->u.ipv6, rule->prefixlen); + /* Note these work even if the underlying nbdkit_peer_* call fails. */ + case PID: + if (family != AF_UNIX) return false; + return nbdkit_peer_pid () == rule->u.id; + + case UID: + if (family != AF_UNIX) return false; + return nbdkit_peer_uid () == rule->u.id; + + case GID: + if (family != AF_UNIX) return false; + return nbdkit_peer_gid () == rule->u.id; + case BAD: default: abort (); @@ -430,8 +485,10 @@ check_if_allowed (const struct sockaddr *addr) { int family = ((struct sockaddr_in *)addr)->sin_family; - /* There's an implicit allow all for non-IP sockets, see the manual. */ - if (family != AF_INET && family != AF_INET6) + /* There's an implicit allow all for non-IP, non-Unix sockets, + * see the manual. + */ + if (family != AF_INET && family != AF_INET6 && family != AF_UNIX) return true; if (matches_rules_list ("ip: match source with allow", @@ -457,7 +514,7 @@ ip_preconnect (nbdkit_next_preconnect *next, void *nxdata, int readonly) /* Follow the rules. */ if (check_if_allowed ((struct sockaddr *) &addr) == false) { nbdkit_error ("client not permitted to connect " - "because of IP address restriction"); + "because of source address restriction"); return -1; } diff --git a/tests/test-ip-filter-gid.sh b/tests/test-ip-filter-gid.sh new file mode 100755 index 00000000..d02407f3 --- /dev/null +++ b/tests/test-ip-filter-gid.sh @@ -0,0 +1,51 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright (C) 2020 Red Hat Inc. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test the ip filter with gid: parameter. + +source ./functions.sh +set -e +set -x + +requires qemu-img --version +# This requires Linux. +requires_linux_kernel_version 2.6 + +nbdkit -U - -v -D ip.rules=1 --filter=ip null allow=gid:`id -g` deny=all \ + --run 'qemu-img info $nbd' + +# This is expected to fail. +if nbdkit -U - -v -D ip.rules=1 --filter=ip null deny=gid:`id -g` \ + --run 'qemu-img info $nbd'; then + echo "$0: expected test to fail" + exit 1 +fi diff --git a/tests/test-ip-filter-pid.sh b/tests/test-ip-filter-pid.sh new file mode 100755 index 00000000..4a7f55a3 --- /dev/null +++ b/tests/test-ip-filter-pid.sh @@ -0,0 +1,70 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright (C) 2020 Red Hat Inc. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test the ip filter with pid: parameter. + +source ./functions.sh +set -e +set -x + +requires nbdinfo --version +requires nbdsh --version +requires_nbdsh_uri +# This requires Linux. +requires_linux_kernel_version 2.6 + +# This is expected to fail because the shell ($$) is not connecting to +# the server. +if nbdkit -U - -v -D ip.rules=1 --filter=ip null allow=pid:$$ deny=all \ + --run 'nbdinfo --size "$uri"'; then + echo "$0: expected test to fail" + exit 1 +fi + +# This is expected to work because we can deny the shell. +nbdkit -U - -v -D ip.rules=1 --filter=ip null deny=pid:$$ \ + --run 'nbdinfo --size "$uri"' + +# This is a better test using nbdsh and passing the PID of nbdsh +# itself to nbdkit. Note this only works because nbd_connect_command +# uses a socketpair which is a kind of nameless Unix domain socket. +nbdsh -c - <<'EOF' +import os + +h.connect_command(["nbdkit", "-s", + "-v", "-D", "ip.rules=1", + "null", "size=512", + "--filter=ip", + "allow=pid:" + str(os.getpid()), + "deny=all"]) +assert h.get_size() == 512 +EOF diff --git a/tests/test-ip-filter-uid.sh b/tests/test-ip-filter-uid.sh new file mode 100755 index 00000000..dc6ab679 --- /dev/null +++ b/tests/test-ip-filter-uid.sh @@ -0,0 +1,51 @@ +#!/usr/bin/env bash +# nbdkit +# Copyright (C) 2020 Red Hat Inc. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: +# +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# +# * Neither the name of Red Hat nor the names of its contributors may be +# used to endorse or promote products derived from this software without +# specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND +# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, +# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR +# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF +# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND +# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, +# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT +# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +# SUCH DAMAGE. + +# Test the ip filter with uid: parameter. + +source ./functions.sh +set -e +set -x + +requires qemu-img --version +# This requires Linux. +requires_linux_kernel_version 2.6 + +nbdkit -U - -v -D ip.rules=1 --filter=ip null allow=uid:`id -u` deny=all \ + --run 'qemu-img info $nbd' + +# This is expected to fail. +if nbdkit -U - -v -D ip.rules=1 --filter=ip null deny=uid:`id -u` \ + --run 'qemu-img info $nbd'; then + echo "$0: expected test to fail" + exit 1 +fi -- 2.27.0

FreeBSD has LOCAL_PEERCRED which is similar to SO_PEERCRED under Linux. It can only be used to read the UID and possibly the GID, but not the PID. --- docs/nbdkit-plugin.pod | 4 +-- filters/ip/nbdkit-ip-filter.pod | 7 ++-- configure.ac | 1 + server/public.c | 64 ++++++++++++++++++++++++++++++--- tests/test-ip-filter-gid.sh | 8 +++-- tests/test-ip-filter-uid.sh | 8 +++-- 6 files changed, 76 insertions(+), 16 deletions(-) diff --git a/docs/nbdkit-plugin.pod b/docs/nbdkit-plugin.pod index e1f10984..ee7b7e3a 100644 --- a/docs/nbdkit-plugin.pod +++ b/docs/nbdkit-plugin.pod @@ -1650,7 +1650,7 @@ C<nbdkit_error> is called and this call returns C<-1>. =head2 C<nbdkit_peer_uid> -(nbdkit E<ge> 1.24, Linux only) +(nbdkit E<ge> 1.24) int64_t nbdkit_peer_uid (void); @@ -1662,7 +1662,7 @@ called and this call returns C<-1>. =head2 C<nbdkit_peer_gid> -(nbdkit E<ge> 1.24, Linux only) +(nbdkit E<ge> 1.24) int64_t nbdkit_peer_gid (void); diff --git a/filters/ip/nbdkit-ip-filter.pod b/filters/ip/nbdkit-ip-filter.pod index d7e0666b..3e63fd28 100644 --- a/filters/ip/nbdkit-ip-filter.pod +++ b/filters/ip/nbdkit-ip-filter.pod @@ -17,7 +17,6 @@ if these are not available. nbdkit E<ge> 1.24 added the ability to filter clients connecting over local Unix domain sockets by client process ID, user ID and group ID. -This currently only works on Linux. =head1 EXAMPLES @@ -128,14 +127,14 @@ could add it as an additional check. =item B<uid:>UID -(nbdkit E<ge> 1.24, Linux only) +(nbdkit E<ge> 1.24) This matches the numeric user ID C<UID>, if the client connects over a Unix domain socket. =item B<gid:>GID -(nbdkit E<ge> 1.24, Linux only) +(nbdkit E<ge> 1.24) This matches the numeric group ID C<GID>, if the client connects over a Unix domain socket. @@ -150,8 +149,6 @@ does nothing. C<AF_VSOCK> connections are always unfiltered. Unix domain sockets were always unfiltered in S<nbdkit E<le> 1.22>. -In S<nbdkit E<ge> 1.24> it is possible to apply filtering to them on -Linux. =head1 PARAMETERS diff --git a/configure.ac b/configure.ac index 3ee4433c..8ec94ef4 100644 --- a/configure.ac +++ b/configure.ac @@ -331,6 +331,7 @@ AC_CHECK_HEADERS([\ sys/procctl.h \ sys/socket.h \ sys/statvfs.h \ + sys/ucred.h \ sys/un.h \ sys/wait.h]) diff --git a/server/public.c b/server/public.c index 0ec33a17..9608600e 100644 --- a/server/public.c +++ b/server/public.c @@ -57,6 +57,14 @@ #include <sys/socket.h> #endif +#ifdef HAVE_SYS_UCRED_H +#include <sys/ucred.h> +#endif + +#ifdef HAVE_SYS_UN_H +#include <sys/un.h> +#endif + #ifdef WIN32 /* For nanosleep on Windows. */ #include <pthread_time.h> @@ -837,11 +845,57 @@ get_peercred (int s, int64_t *pid, int64_t *uid, int64_t *gid) return 0; } -#else /* !SO_PEERCRED */ +#endif /* SO_PEERCRED */ + +#ifdef LOCAL_PEERCRED + +/* FreeBSD supports LOCAL_PEERCRED and struct xucred. */ +static int +get_peercred (int s, int64_t *pid, int64_t *uid, int64_t *gid) +{ + struct xucred xucred; + socklen_t n = sizeof xucred; + + if (getsockopt (s, 0, LOCAL_PEERCRED, &xucred, &n) == -1) { + nbdkit_error ("getsockopt: LOCAL_PEERCRED: %m"); + return -1; + } + + if (xucred.cr_version != XUCRED_VERSION) { + nbdkit_error ("getsockopt: LOCAL_PEERCRED: " + "struct xucred version (%u) " + "did not match expected version (%u)", + xucred.cr_version, XUCRED_VERSION); + return -1; + } + + if (n != sizeof xucred) { + nbdkit_error ("getsockopt: LOCAL_PEERCRED: did not return full struct"); + return -1; + } + + if (pid) + nbdkit_error ("nbdkit_peer_pid is not supported on this platform"); + if (uid && xucred.cr_uid >= 0) { + if (xucred.cr_uid <= INT64_MAX) + *uid = xucred.cr_uid; + else + nbdkit_error ("uid out of range: cannot be mapped to int64_t"); + } + if (gid && xucred.cr_ngroups > 0) { + if (xucred.cr_gid <= INT64_MAX) + *gid = xucred.cr_gid; + else + nbdkit_error ("gid out of range: cannot be mapped to int64_t"); + } + + return 0; +} + +#endif /* LOCAL_PEERCRED */ + +#if !defined(SO_PEERCRED) && !defined(LOCAL_PEERCRED) -/* Note this could be ported to FreeBSD, see LOCAL_PEERCRED in: - * https://www.freebsd.org/cgi/man.cgi?query=unix&sektion=4 - */ static int get_peercred (int s, int64_t *pid, int64_t *uid, int64_t *gid) { @@ -850,7 +904,7 @@ get_peercred (int s, int64_t *pid, int64_t *uid, int64_t *gid) return -1; } -#endif /* !SO_PEERCRED */ +#endif static int get_peercred_common (int64_t *pid, int64_t *uid, int64_t *gid) diff --git a/tests/test-ip-filter-gid.sh b/tests/test-ip-filter-gid.sh index d02407f3..6daa5f2b 100755 --- a/tests/test-ip-filter-gid.sh +++ b/tests/test-ip-filter-gid.sh @@ -37,8 +37,12 @@ set -e set -x requires qemu-img --version -# This requires Linux. -requires_linux_kernel_version 2.6 + +# Not supported on Windows. +if is_windows; then + echo "$0: nbdkit-ip-filter uid: not implemented on Windows" + exit 77 +fi nbdkit -U - -v -D ip.rules=1 --filter=ip null allow=gid:`id -g` deny=all \ --run 'qemu-img info $nbd' diff --git a/tests/test-ip-filter-uid.sh b/tests/test-ip-filter-uid.sh index dc6ab679..430d6b2c 100755 --- a/tests/test-ip-filter-uid.sh +++ b/tests/test-ip-filter-uid.sh @@ -37,8 +37,12 @@ set -e set -x requires qemu-img --version -# This requires Linux. -requires_linux_kernel_version 2.6 + +# Not supported on Windows. +if is_windows; then + echo "$0: nbdkit-ip-filter uid: not implemented on Windows" + exit 77 +fi nbdkit -U - -v -D ip.rules=1 --filter=ip null allow=uid:`id -u` deny=all \ --run 'qemu-img info $nbd' -- 2.27.0