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From: Xin Long <lucien.xin@gmail.com>
To: linux-fsdevel@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>
Cc: NeilBrown <neilb@suse.com>
Subject: Re: [PATCH] seq_read: move count check against iov_iter_count after calling op show
Date: Thu, 28 Jan 2021 17:52:39 +0800	[thread overview]
Message-ID: <CADvbK_eJA5ZaEK928k+jt9QxHAYjZm5Xg7JUG5rCwTSfuGbisA@mail.gmail.com> (raw)
In-Reply-To: <91568e002fed69425485c17de223bef0ff660f3a.1611313420.git.lucien.xin@gmail.com>

Hi,

Anyone working on reviewing this?
Neil?

On Fri, Jan 22, 2021 at 7:03 PM Xin Long <lucien.xin@gmail.com> wrote:
>
> In commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code
> and interface"), it broke a behavior: op show() is always called when op
> next() returns an available obj.
>
> This caused a refcnt leak in net/sctp/proc.c, as of the seq_operations
> sctp_assoc_ops, transport obj is held in op next() and released in op
> show().
>
> Here fix it by moving count check against iov_iter_count after calling
> op show() so that op show() can still be called when op next() returns
> an available obj.
>
> Note that m->index needs to increase so that op start() could go fetch
> the next obj in the next round.
>
> Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface")
> Reported-by: Prijesh <prpatel@redhat.com>
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  fs/seq_file.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/seq_file.c b/fs/seq_file.c
> index 03a369c..da304f7 100644
> --- a/fs/seq_file.c
> +++ b/fs/seq_file.c
> @@ -264,8 +264,6 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
>                 }
>                 if (!p || IS_ERR(p))    // no next record for us
>                         break;
> -               if (m->count >= iov_iter_count(iter))
> -                       break;
>                 err = m->op->show(m, p);
>                 if (err > 0) {          // ->show() says "skip it"
>                         m->count = offs;
> @@ -273,6 +271,10 @@ ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
>                         m->count = offs;
>                         break;
>                 }
> +               if (m->count >= iov_iter_count(iter)) {
> +                       m->index++;
> +                       break;
> +               }
>         }
>         m->op->stop(m, p);
>         n = copy_to_iter(m->buf, m->count, iter);
> --
> 2.1.0
>

  reply	other threads:[~2021-01-28  9:53 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-22 11:03 [PATCH] seq_read: move count check against iov_iter_count after calling op show Xin Long
2021-01-28  9:52 ` Xin Long [this message]
2021-01-28 22:56 ` NeilBrown
2021-01-29  6:57   ` Xin Long
2021-02-04  4:57     ` Xin Long
2021-02-04  5:46       ` NeilBrown
2021-02-04  5:53         ` Xin Long
2021-02-04  6:08 ` [seq_read] 03c44acf0b: xfstests.generic.589.fail kernel test robot

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