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From:   Amir Goldstein <amir73il@gmail.com>
Date:   Tue, 19 Oct 2021 09:02:54 +0300
Message-ID: <CAOQ4uxhQBm3=eVOmcQkvR3AvbdzUAuP1cH6EFrB8YJRQL8WU_g@mail.gmail.com>
Subject: Re: [PATCH v8 26/32] fanotify: WARN_ON against too large file handles
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     Jan Kara <jack@suse.com>, "Darrick J. Wong" <djwong@kernel.org>,
        Theodore Tso <tytso@mit.edu>,
        Dave Chinner <david@fromorbit.com>,
        David Howells <dhowells@redhat.com>,
        Khazhismel Kumykov <khazhy@google.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Ext4 <linux-ext4@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>, kernel@collabora.com
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On Tue, Oct 19, 2021 at 3:03 AM Gabriel Krisman Bertazi
<krisman@collabora.com> wrote:
>
> struct fanotify_error_event, at least, is preallocated and isn't able to
> to handle arbitrarily large file handles.  Future-proof the code by
> complaining loudly if a handle larger than MAX_HANDLE_SZ is ever found.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
>  fs/notify/fanotify/fanotify.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index cedcb1546804..45df610debbe 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -360,13 +360,23 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group,
>  static int fanotify_encode_fh_len(struct inode *inode)
>  {
>         int dwords = 0;
> +       int fh_len;
>
>         if (!inode)
>                 return 0;
>
>         exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
> +       fh_len = dwords << 2;
>
> -       return dwords << 2;
> +       /*
> +        * struct fanotify_error_event might be preallocated and is
> +        * limited to MAX_HANDLE_SZ.  This should never happen, but
> +        * safeguard by forcing an invalid file handle.
> +        */
> +       if (WARN_ON_ONCE(fh_len > MAX_HANDLE_SZ))
> +               return 0;
> +
> +       return fh_len;
>  }
>
>  /*
> --
> 2.33.0
>