[PATCH 5.17 0093/1126] cifs: fix incorrect use of list iterator after the loop

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 04:01:27 EST

From: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>

commit a96c94481f5993eac2271f9fb4d009b7dc076c24 upstream.

The bug is here:
if (!tcon) {
resched = true;

Because the list_for_each_entry() never exits early (without any
break/goto/return inside the loop), the iterator 'ses' after the
loop will always be an pointer to a invalid struct containing the
HEAD (&pserver->smb_ses_list). As a result, the uses of 'ses' above
will lead to a invalid memory access.

The original intention should have been to walk each entry 'ses' in
'&tmp_ses_list', delete '&ses->rlist' and put 'ses'. So fix it with
a list_for_each_entry_safe().

Cc: stable@xxxxxxxxxxxxxxx # 5.17
Fixes: 3663c9045f51a ("cifs: check reconnects for channels of active tcons too")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@xxxxxxxxx>
Reviewed-by: Shyam Prasad N <sprasad@xxxxxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
fs/cifs/smb2pdu.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -3858,8 +3858,10 @@ void smb2_reconnect_server(struct work_s
tcon = kzalloc(sizeof(struct cifs_tcon), GFP_KERNEL);
if (!tcon) {
resched = true;
- list_del_init(&ses->rlist);
- cifs_put_smb_ses(ses);
+ list_for_each_entry_safe(ses, ses2, &tmp_ses_list, rlist) {
+ list_del_init(&ses->rlist);
+ cifs_put_smb_ses(ses);
+ }
goto done;