[PATCH 3.2 047/140] nfsd: auth: Fix gid sorting when rootsquash enabled

Ben Hutchings
2018-02-28T15:24:10Z

From: Ben Hutchings <ben.hutchings@codethink.co.uk>

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>
---
fs/nfsd/auth.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/nfsd/auth.c
+++ b/fs/nfsd/auth.c
@@ -60,10 +60,10 @@ int nfsd_setuser(struct svc_rqst *rqstp,
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);
}