[PATCH] cifs: fix incorrect use of list iterator after the loop

[Steve French]

cc:stable too?

On Tue, Mar 22, 2022 at 1:09 AM Shyam Prasad N via samba-technical
<samba-technical at lists.samba.org> wrote:
>
> On Mon, Mar 21, 2022 at 3:50 PM Xiaomeng Tong <xiam0nd.tong at 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 at 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 at microsoft.com>
>
> Steve, This one needs to be marked for CC stable 5.17+
>
> --
> Regards,
> Shyam
>


-- 
Thanks,

Steve