From 28b5ba2aa0f55d80adb2624564ed2b170c19519e Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Wed, 21 Jun 2017 10:47:15 +0200 Subject: net: introduce SO_PEERGROUPS getsockopt This adds the new getsockopt(2) option SO_PEERGROUPS on SOL_SOCKET to retrieve the auxiliary groups of the remote peer. It is designed to naturally extend SO_PEERCRED. That is, the underlying data is from the same credentials. Regarding its syntax, it is based on SO_PEERSEC. That is, if the provided buffer is too small, ERANGE is returned and @optlen is updated. Otherwise, the information is copied, @optlen is set to the actual size, and 0 is returned. While SO_PEERCRED (and thus `struct ucred') already returns the primary group, it lacks the auxiliary group vector. However, nearly all access controls (including kernel side VFS and SYSVIPC, but also user-space polkit, DBus, ...) consider the entire set of groups, rather than just the primary group. But this is currently not possible with pure SO_PEERCRED. Instead, user-space has to work around this and query the system database for the auxiliary groups of a UID retrieved via SO_PEERCRED. Unfortunately, there is no race-free way to query the auxiliary groups of the PID/UID retrieved via SO_PEERCRED. Hence, the current user-space solution is to use getgrouplist(3p), which itself falls back to NSS and whatever is configured in nsswitch.conf(3). This effectively checks which groups we *would* assign to the user if it logged in *now*. On normal systems it is as easy as reading /etc/group, but with NSS it can resort to quering network databases (eg., LDAP), using IPC or network communication. Long story short: Whenever we want to use auxiliary groups for access checks on IPC, we need further IPC to talk to the user/group databases, rather than just relying on SO_PEERCRED and the incoming socket. This is unfortunate, and might even result in dead-locks if the database query uses the same IPC as the original request. So far, those recursions / dead-locks have been avoided by using primitive IPC for all crucial NSS modules. However, we want to avoid re-inventing the wheel for each NSS module that might be involved in user/group queries. Hence, we would preferably make DBus (and other IPC that supports access-management based on groups) work without resorting to the user/group database. This new SO_PEERGROUPS ioctl would allow us to make dbus-daemon work without ever calling into NSS. Cc: Michal Sekletar Cc: Simon McVittie Reviewed-by: Tom Gundersen Signed-off-by: David Herrmann Signed-off-by: David S. Miller --- net/core/sock.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'net/core') diff --git a/net/core/sock.c b/net/core/sock.c index ad8a4bc84126..6f4b090241c1 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1078,6 +1078,18 @@ static void cred_to_ucred(struct pid *pid, const struct cred *cred, } } +static int groups_to_user(gid_t __user *dst, const struct group_info *src) +{ + struct user_namespace *user_ns = current_user_ns(); + int i; + + for (i = 0; i < src->ngroups; i++) + if (put_user(from_kgid_munged(user_ns, src->gid[i]), dst + i)) + return -EFAULT; + + return 0; +} + int sock_getsockopt(struct socket *sock, int level, int optname, char __user *optval, int __user *optlen) { @@ -1231,6 +1243,27 @@ int sock_getsockopt(struct socket *sock, int level, int optname, goto lenout; } + case SO_PEERGROUPS: + { + int ret, n; + + if (!sk->sk_peer_cred) + return -ENODATA; + + n = sk->sk_peer_cred->group_info->ngroups; + if (len < n * sizeof(gid_t)) { + len = n * sizeof(gid_t); + return put_user(len, optlen) ? -EFAULT : -ERANGE; + } + len = n * sizeof(gid_t); + + ret = groups_to_user((gid_t __user *)optval, + sk->sk_peer_cred->group_info); + if (ret) + return ret; + goto lenout; + } + case SO_PEERNAME: { char address[128]; -- cgit v1.2.3