Backport few dfs related fixes to cifs

Recently we have been seeing kernel panic in cifs_reconnect function while accessing tgt_list. Looks like tgt_list is not initialized correctly. There are fixes already present in 5.10 and later trees. Backporting them to 5.4

CIFS VFS: \\172.30.1.14 cifs_reconnect: no target servers for DFS failover

 BUG: unable to handle page fault for address: fffffffffffffff8
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 260e067 P4D 260e067 PUD 2610067 PMD 0
 Oops: 0000 [#1] SMP PTI
 RIP: 0010:cifs_reconnect+0x51d/0xef0 [cifs]
 RSP: 0018:ffffc90000693da0 EFLAGS: 00010282
 RAX: fffffffffffffff8 RBX: ffff8887fa63b800 RCX: fffffffffffffff8
 Call Trace:
 cifs_handle_standard+0x18d/0x1b0 [cifs]
 cifs_demultiplex_thread+0xa5c/0xc90 [cifs]
 kthread+0x113/0x130

Paulo Alcantara (2):
cifs: get rid of unused parameter in reconn_setup_dfs_targets()
cifs: handle empty list of targets in cifs_reconnect()

 fs/cifs/connect.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

2.39.2

From: Paulo Alcantara <[email protected]>

commit baf3f08ef4083b76ca67b143e135213a7f941879 upstream.

The target iterator parameter "it" is not used in reconn_setup_dfs_targets(), so just remove it.

---
 fs/cifs/connect.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

index 6c8dd7c0b83a..b5cd3dc479ce 100644
@@ -469,8 +469,7 @@ static void reconn_inval_dfs_target(struct TCP_Server_Info *server,
 }
 
 static inline int reconn_setup_dfs_targets(struct cifs_sb_info *cifs_sb,
-					   struct dfs_cache_tgt_list *tl,
-					   struct dfs_cache_tgt_iterator **it)
+					   struct dfs_cache_tgt_list *tl)
 {
 	if (!cifs_sb->origin_fullpath)
 		return -EOPNOTSUPP;

@@ -515,7 +514,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 	} else {
 		cifs_sb = CIFS_SB(sb);
 
-		rc = reconn_setup_dfs_targets(cifs_sb, &tgt_list, &tgt_it);
+		rc = reconn_setup_dfs_targets(cifs_sb, &tgt_list);
 		if (rc && (rc != -EOPNOTSUPP)) {
 			cifs_server_dbg(VFS, "%s: no target servers for DFS failover\n",
 				 __func__);

2.39.2

When passing on patches from other people, you too have to sign-off on the patch, saying that you are ok with it.

Please resend this series with your signed-off on it as well (after reading the documentation to understand what you are agreeing to.)

thanks,

greg k-h

From: Paulo Alcantara <[email protected]>

commit a52930353eaf443489a350a135c5525a4acbbf56 upstream.

In case there were no cached DFS referrals in reconn_setup_dfs_targets(), set cifs_sb to NULL prior to calling reconn_set_next_dfs_target() so it would not try to access an empty tgt_list.

---
 fs/cifs/connect.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

index b5cd3dc479ce..d8d9d9061544 100644
@@ -513,11 +513,13 @@ cifs_reconnect(struct TCP_Server_Info *server)
 		sb = NULL;
 	} else {
 		cifs_sb = CIFS_SB(sb);
-
 		rc = reconn_setup_dfs_targets(cifs_sb, &tgt_list);
-		if (rc && (rc != -EOPNOTSUPP)) {
-			cifs_server_dbg(VFS, "%s: no target servers for DFS failover\n",
-				 __func__);
+		if (rc) {
+			cifs_sb = NULL;
+			if (rc != -EOPNOTSUPP) {
+				cifs_server_dbg(VFS, "%s: no target servers for DFS failover\n",
+						__func__);
+			}
 		} else {
 			server->nr_targets = dfs_cache_get_nr_tgts(&tgt_list);
 		}

2.39.2