psample: Require 'CAP_NET_ADMIN' when joining "packets" group
...
commit 44ec98ea5ea9cfecd31a5c4cc124703cb5442832 upstream.
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 <stdio.h>
#include <netlink/genl/ctrl.h>
#include <netlink/genl/genl.h>
#include <netlink/socket.h>
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)" <security@ncsc.gov.uk>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231206213102.1824398-2-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>