Fix cifs_limit_bvec_subset() so that it limits the span to the maximum
specified and won't return with a size greater than max_size.

Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Reported-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <smfrench@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
---
 fs/cifs/file.c |    1 +
 1 file changed, 1 insertion(+)


diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index ba7f2e09d6c8..4778614cfccf 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3353,6 +3353,7 @@ static size_t cifs_limit_bvec_subset(const struct iov_iter *iter, size_t max_siz
 	while (n && ix < nbv) {
 		len = min3(n, bvecs[ix].bv_len - skip, max_size);
 		span += len;
+		max_size -= len;
 		nsegs++;
 		ix++;
 		if (span >= max_size || nsegs >= max_segs)

On Mon, May 22, 2023 at 8:22 PM David Howells <dhowells@redhat.com> wrote:
>
> Fix cifs_limit_bvec_subset() so that it limits the span to the maximum
> specified and won't return with a size greater than max_size.
>
> Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
> Reported-by: Shyam Prasad N <sprasad@microsoft.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Steve French <smfrench@gmail.com>
> cc: Rohith Surabattula <rohiths.msft@gmail.com>
> cc: Paulo Alcantara <pc@manguebit.com>
> cc: Tom Talpey <tom@talpey.com>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: linux-cifs@vger.kernel.org
> cc: linux-fsdevel@vger.kernel.org
> ---
>  fs/cifs/file.c |    1 +
>  1 file changed, 1 insertion(+)
>
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index ba7f2e09d6c8..4778614cfccf 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -3353,6 +3353,7 @@ static size_t cifs_limit_bvec_subset(const struct iov_iter *iter, size_t max_siz
>         while (n && ix < nbv) {
>                 len = min3(n, bvecs[ix].bv_len - skip, max_size);
>                 span += len;
> +               max_size -= len;

Shouldn't this decrement happen below, after the span has been
compared with max_size?

>                 nsegs++;
>                 ix++;
>                 if (span >= max_size || nsegs >= max_segs)
>


-- 
Regards,
Shyam

Shyam Prasad N <nspmangalore@gmail.com> wrote:

> > +               max_size -= len;
> 
> Shouldn't this decrement happen below, after the span has been
> compared with max_size?

It probably doesn't matter.  The compiler is free to move it around, but yes
that and ix++ can both be moved down.

David

On Mon, May 22, 2023 at 1:11 PM David Howells <dhowells@redhat.com> wrote:
>
> Shyam Prasad N <nspmangalore@gmail.com> wrote:
>
> > > +               max_size -= len;
> >
> > Shouldn't this decrement happen below, after the span has been
> > compared with max_size?
>
> It probably doesn't matter.  The compiler is free to move it around, but yes
> that and ix++ can both be moved down.

I am not sure I follow - can you explain? It looks like moving it up
vs. down would change behavior


-- 
Thanks,

Steve