linux-kernel - Re: [PATCH] cifs: Fix cifs_limit_bvec_subset() to correctly check the maxmimum size

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Message-ID: <CANT5p=pNFpEj0p+njYw3sVdq9CKgsTdh29Gj6iYDOsMN0ocj1Q@mail.gmail.com>
Date:   Mon, 22 May 2023 22:58:39 +0530
From:   Shyam Prasad N <nspmangalore@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Shyam Prasad N <sprasad@...rosoft.com>,
        Steve French <smfrench@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Paulo Alcantara <pc@...guebit.com>,
        Tom Talpey <tom@...pey.com>, Jeff Layton <jlayton@...nel.org>,
        linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cifs: Fix cifs_limit_bvec_subset() to correctly check the
 maxmimum size

On Mon, May 22, 2023 at 8:22 PM David Howells <dhowells@...hat.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@...rosoft.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Steve French <smfrench@...il.com>
> cc: Rohith Surabattula <rohiths.msft@...il.com>
> cc: Paulo Alcantara <pc@...guebit.com>
> cc: Tom Talpey <tom@...pey.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: linux-cifs@...r.kernel.org
> cc: linux-fsdevel@...r.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