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@xxxxxxxxxxx>
Signed-off-by: Ido Schimmel <idosch@xxxxxxxxxx>
Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231206213102.1824398-2-idosch@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
---
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 482c07f2766b..5913da77c71d 100644
--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -30,7 +30,8 @@ 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;
--
2.40.1
