RE: [PATCH] Replaced read with xread in transport-helper.c to fix SSIZE_MAX overun in t5509

> On Thu, Jan 11, 2018 at 12:40:05AM -0500, Randall S. Becker wrote:
> > diff --git a/transport-helper.c b/transport-helper.c index
> > 3640804..68a4e30 100644
> > --- a/transport-helper.c
> > +++ b/transport-helper.c
> > @@ -1202,7 +1202,7 @@ static int udt_do_read(struct
> unidirectional_transfer *t)
> >                 return 0;       /* No space for more. */
> >
> >         transfer_debug("%s is readable", t->src_name);
> > -       bytes = read(t->src, t->buf + t->bufuse, BUFFERSIZE - t->bufuse);
> > +       bytes = xread(t->src, t->buf + t->bufuse, BUFFERSIZE -
> > + t->bufuse);
> >         if (bytes < 0 && errno != EWOULDBLOCK && errno != EAGAIN &&
> >                 errno != EINTR) {
> >                 error_errno("read(%s) failed", t->src_name);
> 
> After this patch, I don't think we can ever see any of those errno values
> again, as xread() will automatically retry in such a case.
> 
> I think that's OK. In the code before your patch, udt_do_read() would return
> 0 in such a case, giving the caller the opportunity to do something besides
> simply retry the read. But the only caller is udt_copy_task_routine(), which
> would just loop anyway.  It may be worth mentioning that in the commit
> message.
> 
> So your patch is OK.  But we should probably clean up on top, like the patch
> below (on top of yours; though note your patch was whitespace corrupted;
> the tabs were converted to spaces).
> 
> -- >8 --
> Subject: [PATCH] transport-helper: drop read/write errno checks
> 
> Since we use xread() and xwrite() here, EINTR, EAGAIN, and EWOULDBLOCK
> retries are already handled for us, and we will never see these errno values
> ourselves. We can drop these conditions entirely, making the code easier to
> follow.
> 
> Signed-off-by: Jeff King <peff@peff.net>
> ---
>  transport-helper.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/transport-helper.c b/transport-helper.c index
> d48be722a5..fc49567ac4 100644
> --- a/transport-helper.c
> +++ b/transport-helper.c
> @@ -1208,8 +1208,7 @@ static int udt_do_read(struct
> unidirectional_transfer *t)
> 
>  	transfer_debug("%s is readable", t->src_name);
>  	bytes = xread(t->src, t->buf + t->bufuse, BUFFERSIZE - t->bufuse);
> -	if (bytes < 0 && errno != EWOULDBLOCK && errno != EAGAIN &&
> -		errno != EINTR) {
> +	if (bytes < 0) {
>  		error_errno("read(%s) failed", t->src_name);
>  		return -1;
>  	} else if (bytes == 0) {
> @@ -1236,7 +1235,7 @@ static int udt_do_write(struct
> unidirectional_transfer *t)
> 
>  	transfer_debug("%s is writable", t->dest_name);
>  	bytes = xwrite(t->dest, t->buf, t->bufuse);
> -	if (bytes < 0 && errno != EWOULDBLOCK) {
> +	if (bytes < 0) {
>  		error_errno("write(%s) failed", t->dest_name);
>  		return -1;
>  	} else if (bytes > 0) {