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From:   Xiaomeng Tong <xiam0nd.tong@gmail.com>
To:     sfrench@samba.org
Cc:     sprasad@microsoft.com, linux-cifs@vger.kernel.org,
        samba-technical@lists.samba.org, linux-kernel@vger.kernel.org,
        jakobkoschel@gmail.com, Xiaomeng Tong <xiam0nd.tong@gmail.com>
Subject: [PATCH] cifs: fix incorrect use of list iterator after the loop
Date:   Sun, 20 Mar 2022 21:50:15 +0800
Message-Id: <20220320135015.19794-1-xiam0nd.tong@gmail.com>
Precedence: bulk

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().

Fixes: 3663c9045f51a ("cifs: check reconnects for channels of active tcons too")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
---
 fs/cifs/smb2pdu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 7e7909b1ae11..f82d6fcb5c64 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -3858,8 +3858,10 @@ void smb2_reconnect_server(struct work_struct *work)
 	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;
 	}
 

base-commit: 14702b3b2438e2f2d07ae93b5d695c166e5c83d1
-- 
2.17.1