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From:   Chris Perl <cperl@janestreet.com>
To:     linux-nfs@vger.kernel.org
Cc:     Chris Perl <cperl@janestreet.com>
Subject: [PATCH 1/1] NFS: nfs_compare_mount_options always compare auth flavors.
Date:   Fri,  9 Nov 2018 04:02:51 -0500
Message-Id: <20181109090251.14145-2-cperl@janestreet.com>
In-Reply-To: <20181109090251.14145-1-cperl@janestreet.com>
References: <20181109090251.14145-1-cperl@janestreet.com>
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This patch removes the check from nfs_compare_mount_options to see if a
`sec' option was passed for the current mount before comparing auth
flavors and instead just always compares auth flavors.

Consider the following scenario:

You have a server with the address 192.168.1.1 and two exports /export/a
and /export/b.  The first export supports `sys' and `krb5' security, the
second just `sys'.

Assume you start with no mounts from the server.

The following results in EIOs being returned as the kernel nfs client
incorrectly thinks it can share the underlying `struct nfs_server's:

$ mkdir /tmp/{a,b}
$ sudo mount -t nfs -o vers=3,sec=krb5 192.168.1.1:/export/a /tmp/a
$ sudo mount -t nfs -o vers=3          192.168.1.1:/export/b /tmp/b
$ df >/dev/null
df: ‘/tmp/b’: Input/output error
---
 fs/nfs/super.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index ac4b2f005778..5ef2c71348bd 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2409,8 +2409,7 @@ static int nfs_compare_mount_options(const struct super_block *s, const struct n
 		goto Ebusy;
 	if (a->acdirmax != b->acdirmax)
 		goto Ebusy;
-	if (b->auth_info.flavor_len > 0 &&
-	   clnt_a->cl_auth->au_flavor != clnt_b->cl_auth->au_flavor)
+	if (clnt_a->cl_auth->au_flavor != clnt_b->cl_auth->au_flavor)
 		goto Ebusy;
 	return 1;
 Ebusy:
-- 
2.17.1