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References: <20221201160724.2593341-1-cccheng@synology.com>
In-Reply-To: <20221201160724.2593341-1-cccheng@synology.com>
From:   Filipe Manana <fdmanana@kernel.org>
Date:   Mon, 5 Dec 2022 10:44:23 +0000
Message-ID: <CAL3q7H5oet2P9XijTtzPo3joZWdoa3OuD9L-wK9nTEFya2PY8w@mail.gmail.com>
Subject: Re: [PATCH] btrfs: refuse to remount read-write with unsupported
 compat-ro features
To:     Chung-Chiang Cheng <cccheng@synology.com>
Cc:     clm@fb.com, josef@toxicpanda.com, dsterba@suse.com,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        shepjeng@gmail.com, kernel@cccheng.net,
        Johnny Chang <johnnyc@synology.com>
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On Thu, Dec 1, 2022 at 5:07 PM Chung-Chiang Cheng <cccheng@synology.com> wrote:
>
> btrfs with unsupported compat-ro features can only be mounted as
> read-only, but we can make it read-write indirectly through remount.
> Just add the missing check to refuse it.
>
>   mount -o ro /dev/vdb /mnt
>   mount -o remount,rw /mnt
>
> Reported-by: Johnny Chang <johnnyc@synology.com>
> Signed-off-by: Chung-Chiang Cheng <cccheng@synology.com>
> ---
>  fs/btrfs/super.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 5942b9384088..45836a426499 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1991,6 +1991,8 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>         unsigned old_flags = sb->s_flags;
>         unsigned long old_opts = fs_info->mount_opt;
>         unsigned long old_compress_type = fs_info->compress_type;
> +       u64 compat_ro = btrfs_super_compat_ro_flags(fs_info->super_copy);
> +       u64 compat_ro_unsupp = compat_ro & ~BTRFS_FEATURE_COMPAT_RO_SUPP;
>         u64 old_max_inline = fs_info->max_inline;
>         u32 old_thread_pool_size = fs_info->thread_pool_size;
>         u32 old_metadata_ratio = fs_info->metadata_ratio;
> @@ -2107,6 +2109,13 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>                 if (ret)
>                         goto restore;
>         } else {
> +               if (compat_ro_unsupp) {
> +                       btrfs_err(fs_info,
> +                               "cannot remount read-write because of unknown compat_ro features (0x%llx)",
> +                               compat_ro);
> +                       ret = -EINVAL;
> +                       goto restore;
> +               }

Wasn't this already done by the following commit?

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=81d5d61454c365718655cfc87d8200c84e25d596

Thanks.


>                 if (BTRFS_FS_ERROR(fs_info)) {
>                         btrfs_err(fs_info,
>                                 "Remounting read-write after error is not allowed");
> --
> 2.34.1
>