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

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Date:   Tue,  5 Apr 2022 09:14:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiaomeng Tong <xiam0nd.tong@...il.com>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Steve French <stfrench@...rosoft.com>
Subject: [PATCH 5.17 0093/1126] cifs: fix incorrect use of list iterator after the loop

From: Xiaomeng Tong <xiam0nd.tong@...il.com>

commit a96c94481f5993eac2271f9fb4d009b7dc076c24 upstream.

The bug is here:
if (!tcon) {
	resched = true;
	list_del_init(&ses->rlist);
	cifs_put_smb_ses(ses);

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@...r.kernel.org # 5.17
Fixes: 3663c9045f51a ("cifs: check reconnects for channels of active tcons too")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
Reviewed-by: Shyam Prasad N <sprasad@...rosoft.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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;
 	}