linux-kernel - [PATCH 3.16 115/254] nfsd: auth: Fix gid sorting when rootsquash enabled

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Message-ID: <lsq.1519831218.840871204@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Ben Hutchings" <ben.hutchings@...ethink.co.uk>,
        "J. Bruce Fields" <bfields@...hat.com>
Subject: [PATCH 3.16 115/254] nfsd: auth: Fix gid sorting when rootsquash
 enabled

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben.hutchings@...ethink.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@...ethink.co.uk>
Acked-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/nfsd/auth.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/nfsd/auth.c
+++ b/fs/nfsd/auth.c
@@ -59,10 +59,10 @@ 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);
 	}