From 44ec98ea5ea9cfecd31a5c4cc124703cb5442832 Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Wed, 6 Dec 2023 23:31:01 +0200 Subject: psample: Require 'CAP_NET_ADMIN' when joining "packets" group The "psample" generic netlink family notifies sampled packets over the "packets" multicast group. This is problematic since by default generic netlink allows non-root users to listen to these notifications. Fix by marking the group with the 'GENL_UNS_ADMIN_PERM' flag. This will prevent non-root users or root without the 'CAP_NET_ADMIN' capability (in the user namespace owning the network namespace) from joining the group. Tested using [1]. Before: # capsh -- -c ./psample_repo # capsh --drop=cap_net_admin -- -c ./psample_repo After: # capsh -- -c ./psample_repo # capsh --drop=cap_net_admin -- -c ./psample_repo Failed to join "packets" multicast group [1] $ cat psample.c #include #include #include #include int join_grp(struct nl_sock *sk, const char *grp_name) { int grp, err; grp = genl_ctrl_resolve_grp(sk, "psample", grp_name); if (grp < 0) { fprintf(stderr, "Failed to resolve \"%s\" multicast group\n", grp_name); return grp; } err = nl_socket_add_memberships(sk, grp, NFNLGRP_NONE); if (err) { fprintf(stderr, "Failed to join \"%s\" multicast group\n", grp_name); return err; } return 0; } int main(int argc, char **argv) { struct nl_sock *sk; int err; sk = nl_socket_alloc(); if (!sk) { fprintf(stderr, "Failed to allocate socket\n"); return -1; } err = genl_connect(sk); if (err) { fprintf(stderr, "Failed to connect socket\n"); return err; } err = join_grp(sk, "config"); if (err) return err; err = join_grp(sk, "packets"); if (err) return err; return 0; } $ gcc -I/usr/include/libnl3 -lnl-3 -lnl-genl-3 -o psample_repo psample.c Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling") Reported-by: "The UK's National Cyber Security Centre (NCSC)" Signed-off-by: Ido Schimmel Reviewed-by: Jacob Keller Reviewed-by: Jiri Pirko Link: https://lore.kernel.org/r/20231206213102.1824398-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski --- net/psample/psample.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/psample/psample.c b/net/psample/psample.c index 81a794e36f53..c34e902855db 100644 --- a/net/psample/psample.c +++ b/net/psample/psample.c @@ -31,7 +31,8 @@ enum psample_nl_multicast_groups { static const struct genl_multicast_group psample_nl_mcgrps[] = { [PSAMPLE_NL_MCGRP_CONFIG] = { .name = PSAMPLE_NL_MCGRP_CONFIG_NAME }, - [PSAMPLE_NL_MCGRP_SAMPLE] = { .name = PSAMPLE_NL_MCGRP_SAMPLE_NAME }, + [PSAMPLE_NL_MCGRP_SAMPLE] = { .name = PSAMPLE_NL_MCGRP_SAMPLE_NAME, + .flags = GENL_UNS_ADMIN_PERM }, }; static struct genl_family psample_nl_family __ro_after_init; -- cgit v1.2.3 From e03781879a0d524ce3126678d50a80484a513c4b Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Wed, 6 Dec 2023 23:31:02 +0200 Subject: drop_monitor: Require 'CAP_SYS_ADMIN' when joining "events" group The "NET_DM" generic netlink family notifies drop locations over the "events" multicast group. This is problematic since by default generic netlink allows non-root users to listen to these notifications. Fix by adding a new field to the generic netlink multicast group structure that when set prevents non-root users or root without the 'CAP_SYS_ADMIN' capability (in the user namespace owning the network namespace) from joining the group. Set this field for the "events" group. Use 'CAP_SYS_ADMIN' rather than 'CAP_NET_ADMIN' because of the nature of the information that is shared over this group. Note that the capability check in this case will always be performed against the initial user namespace since the family is not netns aware and only operates in the initial network namespace. A new field is added to the structure rather than using the "flags" field because the existing field uses uAPI flags and it is inappropriate to add a new uAPI flag for an internal kernel check. In net-next we can rework the "flags" field to use internal flags and fold the new field into it. But for now, in order to reduce the amount of changes, add a new field. Since the information can only be consumed by root, mark the control plane operations that start and stop the tracing as root-only using the 'GENL_ADMIN_PERM' flag. Tested using [1]. Before: # capsh -- -c ./dm_repo # capsh --drop=cap_sys_admin -- -c ./dm_repo After: # capsh -- -c ./dm_repo # capsh --drop=cap_sys_admin -- -c ./dm_repo Failed to join "events" multicast group [1] $ cat dm.c #include #include #include #include int main(int argc, char **argv) { struct nl_sock *sk; int grp, err; sk = nl_socket_alloc(); if (!sk) { fprintf(stderr, "Failed to allocate socket\n"); return -1; } err = genl_connect(sk); if (err) { fprintf(stderr, "Failed to connect socket\n"); return err; } grp = genl_ctrl_resolve_grp(sk, "NET_DM", "events"); if (grp < 0) { fprintf(stderr, "Failed to resolve \"events\" multicast group\n"); return grp; } err = nl_socket_add_memberships(sk, grp, NFNLGRP_NONE); if (err) { fprintf(stderr, "Failed to join \"events\" multicast group\n"); return err; } return 0; } $ gcc -I/usr/include/libnl3 -lnl-3 -lnl-genl-3 -o dm_repo dm.c Fixes: 9a8afc8d3962 ("Network Drop Monitor: Adding drop monitor implementation & Netlink protocol") Reported-by: "The UK's National Cyber Security Centre (NCSC)" Signed-off-by: Ido Schimmel Reviewed-by: Jacob Keller Reviewed-by: Jiri Pirko Link: https://lore.kernel.org/r/20231206213102.1824398-3-idosch@nvidia.com Signed-off-by: Jakub Kicinski --- include/net/genetlink.h | 2 ++ net/core/drop_monitor.c | 4 +++- net/netlink/genetlink.c | 3 +++ 3 files changed, 8 insertions(+), 1 deletion(-) diff --git a/include/net/genetlink.h b/include/net/genetlink.h index e18a4c0d69ee..c53244f20437 100644 --- a/include/net/genetlink.h +++ b/include/net/genetlink.h @@ -12,10 +12,12 @@ * struct genl_multicast_group - generic netlink multicast group * @name: name of the multicast group, names are per-family * @flags: GENL_* flags (%GENL_ADMIN_PERM or %GENL_UNS_ADMIN_PERM) + * @cap_sys_admin: whether %CAP_SYS_ADMIN is required for binding */ struct genl_multicast_group { char name[GENL_NAMSIZ]; u8 flags; + u8 cap_sys_admin:1; }; struct genl_split_ops; diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c index aff31cd944c2..b240d9aae4a6 100644 --- a/net/core/drop_monitor.c +++ b/net/core/drop_monitor.c @@ -183,7 +183,7 @@ out: } static const struct genl_multicast_group dropmon_mcgrps[] = { - { .name = "events", }, + { .name = "events", .cap_sys_admin = 1 }, }; static void send_dm_alert(struct work_struct *work) @@ -1619,11 +1619,13 @@ static const struct genl_small_ops dropmon_ops[] = { .cmd = NET_DM_CMD_START, .validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP, .doit = net_dm_cmd_trace, + .flags = GENL_ADMIN_PERM, }, { .cmd = NET_DM_CMD_STOP, .validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP, .doit = net_dm_cmd_trace, + .flags = GENL_ADMIN_PERM, }, { .cmd = NET_DM_CMD_CONFIG_GET, diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c index 92ef5ed2e7b0..9c7ffd10df2a 100644 --- a/net/netlink/genetlink.c +++ b/net/netlink/genetlink.c @@ -1691,6 +1691,9 @@ static int genl_bind(struct net *net, int group) if ((grp->flags & GENL_UNS_ADMIN_PERM) && !ns_capable(net->user_ns, CAP_NET_ADMIN)) ret = -EPERM; + if (grp->cap_sys_admin && + !ns_capable(net->user_ns, CAP_SYS_ADMIN)) + ret = -EPERM; break; } -- cgit v1.2.3