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nfs, rpc: Ensure kernel credentials have at least one group

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This fixes several bugs where some 'struct ucred' in the kernel,
constructed from user input (via nmount(2)) or obtained from other
servers (e.g., gssd(8)), could have an unfilled 'cr_groups' field and
whose 'cr_groups[0]' (or 'cr_gid', which is an alias) was later
accessed, causing an uninitialized access giving random access rights.

Use crsetgroups_fallback() to enforce a fallback group when possible.
For NFS, the chosen fallback group is that of the NFS server in the
current VNET (NFSD_VNET(nfsrv_defaultgid)).

There does not seem to be any sensible fallback available in rpc code
(sys/rpc/svc_auth.c, svc_getcred()) on AUTH_UNIX (TLS or not), so just
fail credential retrieval there.  Stock NSS sources, rpc.tlsservd(8) or
rpc.tlsclntd(8) provide non-empty group lists, so will not be impacted.

Discussed with: rmacklem (by mail)
Approved by:    markj (mentor)
MFC after:      3 days
Differential Revision:  https://reviews.freebsd.org/D46918
This commit is contained in:
Olivier Certner 2024-10-02 16:28:59 +02:00
parent d4e0d4d92e
commit cfbe7a62dc
No known key found for this signature in database
GPG Key ID: 8CA13040971E2627
7 changed files with 28 additions and 15 deletions
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4
sys/fs/nfs/nfs_commonport.c
View File

@ -75,6 +75,7 @@ NFSD_VNET_DEFINE(struct nfsstatsv1 *, nfsstatsv1_p);
NFSD_VNET_DECLARE(struct nfssockreq, nfsrv_nfsuserdsock);
NFSD_VNET_DECLARE(nfsuserd_state, nfsrv_nfsuserd);
NFSD_VNET_DECLARE(gid_t, nfsrv_defaultgid);
int nfs_pnfsio(task_fn_t *, void *);
@ -258,7 +259,8 @@ newnfs_copycred(struct nfscred *nfscr, struct ucred *cr)
KASSERT(nfscr->nfsc_ngroups >= 0,
("newnfs_copycred: negative nfsc_ngroups"));
cr->cr_uid = nfscr->nfsc_uid;
crsetgroups(cr, nfscr->nfsc_ngroups, nfscr->nfsc_groups);
crsetgroups_fallback(cr, nfscr->nfsc_ngroups, nfscr->nfsc_groups,
NFSD_VNET(nfsrv_defaultgid));
}
/*

5
sys/fs/nfs/nfs_commonsubs.c
View File

@ -4051,8 +4051,9 @@ nfssvc_idname(struct nfsd_idargs *nidp)
*/
cr = crget();
cr->cr_uid = cr->cr_ruid = cr->cr_svuid = nidp->nid_uid;
crsetgroups(cr, nidp->nid_ngroup, grps);
cr->cr_rgid = cr->cr_svgid = cr->cr_groups[0];
crsetgroups_fallback(cr, nidp->nid_ngroup, grps,
NFSD_VNET(nfsrv_defaultgid));
cr->cr_rgid = cr->cr_svgid = cr->cr_gid;
cr->cr_prison = curthread->td_ucred->cr_prison;
prison_hold(cr->cr_prison);
#ifdef MAC

6
sys/fs/nfsserver/nfs_nfsdport.c
View File

@ -3311,7 +3311,11 @@ nfsd_excred(struct nfsrv_descript *nd, struct nfsexstuff *exp,
NFSVNO_EXPORTANON(exp) ||
(nd->nd_flag & ND_AUTHNONE) != 0) {
nd->nd_cred->cr_uid = credanon->cr_uid;
nd->nd_cred->cr_gid = credanon->cr_gid;
/*
* 'credanon' is already a 'struct ucred' that was built
* internally with calls to crsetgroups_fallback(), so
* we don't need a fallback here.
*/
crsetgroups(nd->nd_cred, credanon->cr_ngroups,
credanon->cr_groups);
} else if ((nd->nd_flag & ND_GSS) == 0) {

6
sys/fs/nfsserver/nfs_nfsdsocket.c
View File

@ -1422,13 +1422,11 @@ static struct ucred *
nfsrv_createrootcred(void)
{
struct ucred *cr;
gid_t grp;
cr = crget();
cr->cr_uid = cr->cr_ruid = cr->cr_svuid = UID_ROOT;
grp = GID_WHEEL;
crsetgroups(cr, 1, &grp);
cr->cr_rgid = cr->cr_svgid = cr->cr_groups[0];
crsetgroups_fallback(cr, 0, NULL, GID_WHEEL);
cr->cr_rgid = cr->cr_svgid = cr->cr_gid;
cr->cr_prison = curthread->td_ucred->cr_prison;
prison_hold(cr->cr_prison);
#ifdef MAC

12
sys/kern/vfs_export.c
View File

@ -61,6 +61,10 @@
#include <rpc/types.h>
#include <rpc/auth.h>
#include <fs/nfs/nfsport.h>
NFSD_VNET_DECLARE(gid_t, nfsrv_defaultgid);
static MALLOC_DEFINE(M_NETADDR, "export_host", "Export host address structure");
#if defined(INET) || defined(INET6)
@ -133,8 +137,8 @@ vfs_hang_addrlist(struct mount *mp, struct netexport *nep,
np->netc_exflags = argp->ex_flags;
np->netc_anon = crget();
np->netc_anon->cr_uid = argp->ex_uid;
crsetgroups(np->netc_anon, argp->ex_ngroups,
argp->ex_groups);
crsetgroups_fallback(np->netc_anon, argp->ex_ngroups,
argp->ex_groups, NFSD_VNET(nfsrv_defaultgid));
np->netc_anon->cr_prison = &prison0;
prison_hold(np->netc_anon->cr_prison);
np->netc_numsecflavors = argp->ex_numsecflavors;
@ -212,8 +216,8 @@ vfs_hang_addrlist(struct mount *mp, struct netexport *nep,
np->netc_exflags = argp->ex_flags;
np->netc_anon = crget();
np->netc_anon->cr_uid = argp->ex_uid;
crsetgroups(np->netc_anon, argp->ex_ngroups,
argp->ex_groups);
crsetgroups_fallback(np->netc_anon, argp->ex_ngroups, argp->ex_groups,
NFSD_VNET(nfsrv_defaultgid));
np->netc_anon->cr_prison = &prison0;
prison_hold(np->netc_anon->cr_prison);
np->netc_numsecflavors = argp->ex_numsecflavors;

2
sys/rpc/rpcsec_gss/svc_rpcsec_gss.c
View File

@ -537,7 +537,7 @@ rpc_gss_svc_getcred(struct svc_req *req, struct ucred **crp, int *flavorp)
cr = client->cl_cred = crget();
cr->cr_uid = cr->cr_ruid = cr->cr_svuid = uc->uid;
cr->cr_rgid = cr->cr_svgid = uc->gid;
crsetgroups(cr, uc->gidlen, uc->gidlist);
crsetgroups_fallback(cr, uc->gidlen, uc->gidlist, uc->gid);
cr->cr_prison = curthread->td_ucred->cr_prison;
prison_hold(cr->cr_prison);
*crp = crhold(cr);

8
sys/rpc/svc_auth.c
View File

@ -187,10 +187,12 @@ svc_getcred(struct svc_req *rqst, struct ucred **crp, int *flavorp)
if ((xprt->xp_tls & (RPCTLS_FLAGS_CERTUSER |
RPCTLS_FLAGS_DISABLED)) == RPCTLS_FLAGS_CERTUSER &&
flavor == AUTH_UNIX) {
if (xprt->xp_ngrps <= 0)
return (FALSE);
cr = crget();
cr->cr_uid = cr->cr_ruid = cr->cr_svuid = xprt->xp_uid;
crsetgroups(cr, xprt->xp_ngrps, xprt->xp_gidp);
cr->cr_rgid = cr->cr_svgid = xprt->xp_gidp[0];
cr->cr_rgid = cr->cr_svgid = cr->cr_gid;
cr->cr_prison = curthread->td_ucred->cr_prison;
prison_hold(cr->cr_prison);
*crp = cr;
@ -200,10 +202,12 @@ svc_getcred(struct svc_req *rqst, struct ucred **crp, int *flavorp)
switch (flavor) {
case AUTH_UNIX:
xcr = (struct xucred *) rqst->rq_clntcred;
if (xcr->cr_ngroups <= 0)
return (FALSE);
cr = crget();
cr->cr_uid = cr->cr_ruid = cr->cr_svuid = xcr->cr_uid;
crsetgroups(cr, xcr->cr_ngroups, xcr->cr_groups);
cr->cr_rgid = cr->cr_svgid = cr->cr_groups[0];
cr->cr_rgid = cr->cr_svgid = cr->cr_gid;
cr->cr_prison = curthread->td_ucred->cr_prison;
prison_hold(cr->cr_prison);
*crp = cr;