Re: [PATCH] net: sunrpc: xprt.c: fix shift-out-of-bounds in xprt_calc_majortimeo

[Trond Myklebust <trondmy@hammerspace.com>]

On Mon, 2021-04-19 at 16:36 +0000, Kurt Manucredo wrote:
> Fix shift-out-of-bounds in xprt_calc_majortimeo().
> 
> UBSAN: shift-out-of-bounds in net/sunrpc/xprt.c:658:14
> shift exponent 536871232 is too large for 64-bit type 'long u
> 
> Reported-by: syzbot+ba2e91df8f74809417fa@syzkaller.appspotmail.com
> Signed-off-by: Kurt Manucredo <fuzzybritches0@gmail.com>
> ---
>  net/sunrpc/xprt.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index 691ccf8049a4..07128ac3d51d 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -655,7 +655,10 @@ static unsigned long xprt_calc_majortimeo(struct
> rpc_rqst *req)
>         unsigned long majortimeo = req->rq_timeout;
>  
>         if (to->to_exponential)
> -               majortimeo <<= to->to_retries;
> +               if (to->to_retries >= sizeof(majortimeo) * 8)
> +                       majortimeo = to->to_maxval;
> +               else
> +                       majortimeo <<= to->to_retries;
>         else
>                 majortimeo += to->to_increment * to->to_retries;
>         if (majortimeo > to->to_maxval || majortimeo == 0)

I've already stated on the mailing list that I'm not accepting any
changes to xprt_calc_majortimeo() for this problem. There is a fix to
the NFS mount code that addresses this bounds issue, and that commit is
already being tested in linux-next.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com