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References: <20220320135015.19794-1-xiam0nd.tong@gmail.com>
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From:   Shyam Prasad N <nspmangalore@gmail.com>
Date:   Tue, 22 Mar 2022 11:37:08 +0530
Message-ID: <CANT5p=qEmVtgC5gD5G3D1o+7mxLMpQawnh0DSY+dLD-Dyrw5Uw@mail.gmail.com>
Subject: Re: [PATCH] cifs: fix incorrect use of list iterator after the loop
To:     Xiaomeng Tong <xiam0nd.tong@gmail.com>
Cc:     Steven French <sfrench@samba.org>, sprasad@microsoft.com,
        CIFS <linux-cifs@vger.kernel.org>,
        samba-technical <samba-technical@lists.samba.org>,
        LKML <linux-kernel@vger.kernel.org>, jakobkoschel@gmail.com
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On Mon, Mar 21, 2022 at 3:50 PM Xiaomeng Tong <xiam0nd.tong@gmail.com> wrote:
>
> 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
>

Hi Xiaomeng,
Good catch.
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>

Steve, This one needs to be marked for CC stable 5.17+

-- 
Regards,
Shyam