linux-kernel - Re: [PATCH] gfs2: Move a variable assignment behind a null pointer check in inode_go

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Message-ID: <CAHc6FU4RekTwC9jH-H898PCyufrE59NYqZWy_V3p7R7dOCaTDA@mail.gmail.com>
Date:   Tue, 18 Apr 2023 14:51:05 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Markus Elfring <Markus.Elfring@....de>
Cc:     kernel-janitors@...r.kernel.org, cluster-devel@...hat.com,
        Bob Peterson <rpeterso@...hat.com>, cocci@...ia.fr,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gfs2: Move a variable assignment behind a null pointer
 check in inode_go_dump()

Hi Markus,

On Thu, Apr 13, 2023 at 9:23 PM Markus Elfring <Markus.Elfring@....de> wrote:
> Date: Thu, 13 Apr 2023 20:54:30 +0200
>
> The address of a data structure member was determined before
> a corresponding null pointer check in the implementation of
> the function “inode_go_dump”.
>
> Thus avoid the risk for undefined behaviour by moving the assignment
> for the variable “inode” behind the null pointer check.
>
> This issue was detected by using the Coccinelle software.
>
> Fixes: 27a2660f1ef944724956d92e8a312b6da0936fae ("gfs2: Dump nrpages for inodes and their glocks")

Okay, that's a worthwhile cleanup. It doesn't actually fix a bug, so
I'm not going to add a Fixes tag, though.

> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  fs/gfs2/glops.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/gfs2/glops.c b/fs/gfs2/glops.c
> index b65950e76be5..6e33c8058059 100644
> --- a/fs/gfs2/glops.c
> +++ b/fs/gfs2/glops.c
> @@ -535,12 +535,13 @@ static void inode_go_dump(struct seq_file *seq, struct gfs2_glock *gl,
>                           const char *fs_id_buf)
>  {
>         struct gfs2_inode *ip = gl->gl_object;
> -       struct inode *inode = &ip->i_inode;
> +       struct inode *inode;
>         unsigned long nrpages;
>
>         if (ip == NULL)
>                 return;
>
> +       inode = &ip->i_inode;
>         xa_lock_irq(&inode->i_data.i_pages);
>         nrpages = inode->i_data.nrpages;
>         xa_unlock_irq(&inode->i_data.i_pages);
> --
> 2.40.0
>

Thanks,
Andreas