Re: [PATCH v1] CIFS: fix deadlock in cached root handling

[Steve French <smfrench@gmail.com>]

added cc: stable and made minor cleanup of missing tab

On Wed, Jul 17, 2019 at 1:38 PM Pavel Shilovsky <piastryyy@gmail.com> wrote:
>
> Looks good.
>
> Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
>
> --
> Best regards,
> Pavel Shilovsky
>
> ср, 17 июл. 2019 г. в 03:46, Aurelien Aptel <aaptel@suse.com>:
> >
> > Prevent deadlock between open_shroot() and
> > cifs_mark_open_files_invalid() by releasing the lock before entering
> > SMB2_open, taking it again after and checking if we still need to use
> > the result.
> >
> > Link: https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@prodrive-technologies.com/T/#u
> > Fixes: 3d4ef9a15343 ("smb3: fix redundant opens on root")
> > Signed-off-by: Aurelien Aptel <aaptel@suse.com>
> > ---
> >
> > this is the for-next version of the patch I sent in the thread
> > https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@prodrive-technologies.com/T/#u
> >
> >
> >  fs/cifs/smb2ops.c | 46 +++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 45 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> > index 6cb4def11ebe..8202c996b55e 100644
> > --- a/fs/cifs/smb2ops.c
> > +++ b/fs/cifs/smb2ops.c
> > @@ -694,8 +694,51 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
> >
> >         smb2_set_related(&rqst[1]);
> >
> > +       /*
> > +        * We do not hold the lock for the open because in case
> > +        * SMB2_open needs to reconnect, it will end up calling
> > +        * cifs_mark_open_files_invalid() which takes the lock again
> > +        * thus causing a deadlock
> > +        */
> > +
> > +       mutex_unlock(&tcon->crfid.fid_mutex);
> >         rc = compound_send_recv(xid, ses, flags, 2, rqst,
> >                                 resp_buftype, rsp_iov);
> > +       mutex_lock(&tcon->crfid.fid_mutex);
> > +
> > +       /*
> > +        * Now we need to check again as the cached root might have
> > +        * been successfully re-opened from a concurrent process
> > +        */
> > +
> > +       if (tcon->crfid.is_valid) {
> > +               /* work was already done */
> > +
> > +               /* stash fids for close() later */
> > +               struct cifs_fid fid = {
> > +                       .persistent_fid = pfid->persistent_fid,
> > +                       .volatile_fid = pfid->volatile_fid,
> > +               };
> > +
> > +               /*
> > +                * caller expects this func to set pfid to a valid
> > +                * cached root, so we copy the existing one and get a
> > +                * reference.
> > +                */
> > +               memcpy(pfid, tcon->crfid.fid, sizeof(*pfid));
> > +               kref_get(&tcon->crfid.refcount);
> > +
> > +               mutex_unlock(&tcon->crfid.fid_mutex);
> > +
> > +               if (rc == 0) {
> > +                       /* close extra handle outside of crit sec */
> > +                       SMB2_close(xid, tcon, fid.persistent_fid, fid.volatile_fid);
> > +               }
> > +              goto oshr_free;
> > +       }
> > +
> > +       /* Cached root is still invalid, continue normaly */
> > +
> >         if (rc)
> >                 goto oshr_exit;
> >
> > @@ -729,8 +772,9 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
> >                                 (char *)&tcon->crfid.file_all_info))
> >                 tcon->crfid.file_all_info_is_valid = 1;
> >
> > - oshr_exit:
> > +oshr_exit:
> >         mutex_unlock(&tcon->crfid.fid_mutex);
> > +oshr_free:
> >         SMB2_open_free(&rqst[0]);
> >         SMB2_query_info_free(&rqst[1]);
> >         free_rsp_buf(resp_buftype[0], rsp_iov[0].iov_base);
> > --
> > 2.16.4
> >



-- 
Thanks,

Steve