[PATCH] smb/client: avoid possible NULL dereference in cifs_free_subrequest()

[Steve French]

Tentatively merged into cifs-2.6.git pending review/testing

Did minor update to add Cc: stable

On Thu, Aug 8, 2024 at 7:26 AM Su Hui <suhui at nfschina.com> wrote:
>
> Clang static checker (scan-build) warning:
>         cifsglob.h:line 890, column 3
>         Access to field 'ops' results in a dereference of a null pointer.
>
> Commit 519be989717c ("cifs: Add a tracepoint to track credits involved in
> R/W requests") adds a check for 'rdata->server', and let clang throw this
> warning about NULL dereference.
>
> When 'rdata->credits.value != 0 && rdata->server == NULL' happens,
> add_credits_and_wake_if() will call rdata->server->ops->add_credits().
> This will cause NULL dereference problem. Add a check for 'rdata->server'
> to avoid NULL dereference.
>
> Signed-off-by: Su Hui <suhui at nfschina.com>
> ---
>  fs/smb/client/file.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
> index b2405dd4d4d4..45459af5044d 100644
> --- a/fs/smb/client/file.c
> +++ b/fs/smb/client/file.c
> @@ -315,7 +315,7 @@ static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)
>  #endif
>         }
>
> -       if (rdata->credits.value != 0)
> +       if (rdata->credits.value != 0) {
>                 trace_smb3_rw_credits(rdata->rreq->debug_id,
>                                       rdata->subreq.debug_index,
>                                       rdata->credits.value,
> @@ -323,8 +323,12 @@ static void cifs_free_subrequest(struct netfs_io_subrequest *subreq)
>                                       rdata->server ? rdata->server->in_flight : 0,
>                                       -rdata->credits.value,
>                                       cifs_trace_rw_credits_free_subreq);
> +               if (rdata->server)
> +                       add_credits_and_wake_if(rdata->server, &rdata->credits, 0);
> +               else
> +                       rdata->credits.value = 0;
> +       }
>
> -       add_credits_and_wake_if(rdata->server, &rdata->credits, 0);
>         if (rdata->have_xid)
>                 free_xid(rdata->xid);
>  }
> --
> 2.30.2
>
>


-- 
Thanks,

Steve