[PATCH 5.6 32/49] cifs: do not share tcons with DFS

[Greg Kroah-Hartman]

From: Paulo Alcantara <pc@xxxxxx>

[ Upstream commit 65303de829dd6d291a4947c1a31de31896f8a060 ]

This disables tcon re-use for DFS shares.

tcon->dfs_path stores the path that the tcon should connect to when
doing failing over.

If that tcon is used multiple times e.g. 2 mounts using it with
different prefixpath, each will need a different dfs_path but there is
only one tcon. The other solution would be to split the tcon in 2
tcons during failover but that is much harder.

tcons could not be shared with DFS in cifs.ko because in a
DFS namespace like:

          //domain/dfsroot -> /serverA/dfsroot, /serverB/dfsroot

          //serverA/dfsroot/link -> /serverA/target1/aa/bb

          //serverA/dfsroot/link2 -> /serverA/target1/cc/dd

you can see that link and link2 are two DFS links that both resolve to
the same target share (/serverA/target1), so cifs.ko will only contain a
single tcon for both link and link2.

The problem with that is, if we (auto)mount "link" and "link2", cifs.ko
will only contain a single tcon for both DFS links so we couldn't
perform failover or refresh the DFS cache for both links because
tcon->dfs_path was set to either "link" or "link2", but not both --
which is wrong.

Signed-off-by: Paulo Alcantara (SUSE) <pc@xxxxxx>
Reviewed-by: Aurelien Aptel <aaptel@xxxxxxxx>
Reviewed-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/cifs/connect.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index d4a23b48e24d8..9c614d6916c2d 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3419,6 +3419,10 @@ cifs_find_tcon(struct cifs_ses *ses, struct smb_vol *volume_info)
 	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each(tmp, &ses->tcon_list) {
 		tcon = list_entry(tmp, struct cifs_tcon, tcon_list);
+#ifdef CONFIG_CIFS_DFS_UPCALL
+		if (tcon->dfs_path)
+			continue;
+#endif
 		if (!match_tcon(tcon, volume_info))
 			continue;
 		++tcon->tc_count;
-- 
2.20.1