nfsd: auth: Fix gid sorting when rootsquash enabled

commit 1995266727fa8143897e89b55f5d3c79aa828420 upstream.

Commit bdcf0a423ea1 ("kernel: make groups_sort calling a responsibility
group_info allocators") appears to break nfsd rootsquash in a pretty
major way.

It adds a call to groups_sort() inside the loop that copies/squashes
gids, which means the valid gids are sorted along with the following
garbage.  The net result is that the highest numbered valid gids are
replaced with any lower-valued garbage gids, possibly including 0.

We should sort only once, after filling in all the gids.

Fixes: bdcf0a423ea1 ("kernel: make groups_sort calling a responsibility ...")
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Acked-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/nfsd/auth.c b/fs/nfsd/auth.c
index 46ef7f5..3d3f14c 100644 (file)
--- a/fs/nfsd/auth.c
+++ b/fs/nfsd/auth.c
@@ -60,10 +60,10 @@ int nfsd_setuser(struct svc_rqst *rqstp, struct svc_export *exp)
                                GROUP_AT(gi, i) = exp->ex_anon_gid;
                        else
                                GROUP_AT(gi, i) = GROUP_AT(rqgi, i);
-
-                       /* Each thread allocates its own gi, no race */
-                       groups_sort(gi);
                }
+
+               /* Each thread allocates its own gi, no race */
+               groups_sort(gi);
        } else {
                gi = get_group_info(rqgi);
        }