[PATCH 4.19 209/313] NFS: nfs_compare_mount_options always compare auth flavors.

From: Greg Kroah-Hartman
Date: Mon Feb 11 2019 - 09:48:41 EST

4.19-stable review patch. If anyone has any objections, please let me know.


[ Upstream commit 594d1644cd59447f4fceb592448d5cd09eb09b5e ]

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 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 /tmp/a
$ sudo mount -t nfs -o vers=3 /tmp/b
$ df >/dev/null
df: â/tmp/bâ: Input/output error

Signed-off-by: Chris Perl <cperl@xxxxxxxxxxxxxx>
Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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;