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From:   Scott Mayhew <smayhew@redhat.com>
To:     trond.myklebust@hammerspace.com, anna.schumaker@netapp.com
Cc:     ps@pks.im, dhowells@redhat.com, linux-nfs@vger.kernel.org
Subject: [PATCH] NFS: Ensure the fs_context has the correct fs_type before mounting
Date:   Fri, 21 Feb 2020 15:21:38 -0500
Message-Id: <20200221202138.3744133-1-smayhew@redhat.com>
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Sender: linux-nfs-owner@vger.kernel.org
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This is necessary because unless userspace explicitly requests fstype
"nfs4" (either via "mount -t nfs4" or by calling the "mount.nfs4" helper
directly), the fstype will default to "nfs".

This was fine on older kernels because the super_block->s_type was set
via mount_info->nfs_mod->nfs_fs, which was set when parsing the mount
options and subsequently passed in the "type" argument of sget().

After commit f2aedb713c28 ("NFS: Add fs_context support."), sget_fc(),
which has no "type" argument, is called instead.  In sget_fc(), the
super_block->s_type is set via fs_context->fs_type, which was set when
the filesystem context was initially created.

Reported-by: Patrick Steinhardt <ps@pks.im>
Fixes: f2aedb713c28 ("NFS: Add fs_context support.")
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
---
 fs/nfs/fs_context.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index e1b938457ab9..b616263b0eb6 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -1240,6 +1240,13 @@ static int nfs_fs_context_validate(struct fs_conte=
xt *fc)
 		}
 		ctx->nfs_mod =3D nfs_mod;
 	}
+
+	/* Ensure the filesystem context has the correct fs_type */
+	if (fc->fs_type !=3D ctx->nfs_mod->nfs_fs) {
+		module_put(fc->fs_type->owner);
+		__module_get(ctx->nfs_mod->nfs_fs->owner);
+		fc->fs_type =3D ctx->nfs_mod->nfs_fs;
+	}
 	return 0;
=20
 out_no_device_name:
--=20
2.24.1