linux-kernel - Re: [PATCH] fs: affs: fix a NULL pointer dereference

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Date:   Tue, 19 Mar 2019 14:43:04 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Kangjie Lu <kjlu@....edu>
Cc:     pakki001@....edu, David Sterba <dsterba@...e.com>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: affs: fix a NULL pointer dereference

Hi Kangjie,

On Thu, Mar 14, 2019 at 8:47 AM Kangjie Lu <kjlu@....edu> wrote:
> If affs_bread fails, do not use ext_bh to avoid NULL pointer
>  dereference
>
> Signed-off-by: Kangjie Lu <kjlu@....edu>

Thanks for your patch!

> --- a/fs/affs/file.c
> +++ b/fs/affs/file.c
> @@ -835,7 +835,7 @@ void
>  affs_truncate(struct inode *inode)
>  {
>         struct super_block *sb = inode->i_sb;
> -       u32 ext, ext_key;
> +       u32 ext, ext_key, ext_bk;

Why adding an intermediate variable (without __be32 tag)?

>         u32 last_blk, blkcnt, blk;
>         u32 size;
>         struct buffer_head *ext_bh;
> @@ -941,8 +941,12 @@ affs_truncate(struct inode *inode)
>                 size = AFFS_SB(sb)->s_hashsize;
>                 if (size > blkcnt - blk)
>                         size = blkcnt - blk;
> -               for (i = 0; i < size; i++, blk++)
> -                       affs_free_block(sb, be32_to_cpu(AFFS_BLOCK(sb, ext_bh, i)));
> +               if (ext_bh) {
> +                       for (i = 0; i < size; i++, blk++) {
> +                               ext_bk = AFFS_BLOCK(sb, ext_bh, i);
> +                               affs_free_block(sb, be32_to_cpu(ext_bk));
> +                       }

Now this ignores all errors, silently.
What about handling actual errors, and propagating them up?

> +               }
>                 affs_free_block(sb, ext_key);
>                 ext_key = be32_to_cpu(AFFS_TAIL(sb, ext_bh)->extension);
>                 affs_brelse(ext_bh);

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds