[PATCH AUTOSEL 5.6 63/79] cifs: do not share tcons with DFS

Sasha Levin
2020-04-30T14:08:16Z

From: Paulo Alcantara <pc@cjr.nz>

[ 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@cjr.nz>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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