7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ameer Hamza commit a12cc0930235b86b934ade7c077a1935c2ac333d upstream. When rpc.mountd cannot resolve a uid (getpwuid() or getgrouplist() failure, e.g. while winbind or sssd is briefly unreachable), it answers the auth.unix.gid upcall with zero groups. unix_gid_parse() installs that as a valid positive entry, and svcauth_unix_set_client() then replaces the credential's group list with the empty one on every request, RPCSEC_GSS included via svcauth_gss_set_client(). One failed lookup strips that uid of all supplementary groups on every export for up to mountd's configured TTL (30 minutes by default), long after the NSS backend has recovered. mountd cannot send an empty list for a successful lookup, since getgrouplist(3) always includes at least the user's primary group, so a zero-group reply can only mean the lookup failed. Record it as a negative entry: unix_gid_find() then returns -ENOENT and svcauth_unix_set_client() keeps the groups the RPC credential already carries. This is the fallback that commit 3fc605a2aa38 ("[PATCH] knfsd: allow the server to provide a gid list when using AUTH_UNIX authentication") promised when no answer is available, and the same state try_to_negate_entry() already creates when no listener holds the channel open. Fixes: 3fc605a2aa38 ("[PATCH] knfsd: allow the server to provide a gid list when using AUTH_UNIX authentication") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-fable-5 Signed-off-by: Ameer Hamza Link: https://patch.msgid.link/20260814221953.108837-2-ameer.hamza@truenas.com Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman --- net/sunrpc/svcauth_unix.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/net/sunrpc/svcauth_unix.c +++ b/net/sunrpc/svcauth_unix.c @@ -540,6 +540,13 @@ static int unix_gid_parse(struct cache_d if (ugp) { struct cache_head *ch; ug.h.flags = 0; + /* + * mountd sends at least the user's primary group on + * success, so an empty list can only mean the lookup + * failed. Keep the credential's own groups instead. + */ + if (gids == 0) + set_bit(CACHE_NEGATIVE, &ug.h.flags); ug.h.expiry_time = expiry; ch = sunrpc_cache_update(cd, &ug.h, &ugp->h,