Re: [PATCH -next 4/5] gfs2: fix possible null-ptr-deref when parsing param

[Andreas Grünbacher]

Am So., 23. Okt. 2022 um 18:46 Uhr schrieb Hawkins Jiawei <yin31149@xxxxxxxxx>:
> According to commit "vfs: parse: deal with zero length string value",
> kernel will set the param->string to null pointer in vfs_parse_fs_string()
> if fs string has zero length.
>
> Yet the problem is that, gfs2_parse_param() will dereferences the
> param->string, without checking whether it is a null pointer, which may
> trigger a null-ptr-deref bug.
>
> This patch solves it by adding sanity check on param->string
> in gfs2_parse_param().

Yes, but then it dereferences param->string in the error message. That
won't help.

> Reported-by: syzbot+da97a57c5b742d05db51@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: syzbot+da97a57c5b742d05db51@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: agruenba@xxxxxxxxxx
> Cc: cluster-devel@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: rpeterso@xxxxxxxxxx
> Cc: syzkaller-bugs@xxxxxxxxxxxxxxxx
> Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
> ---
>  fs/gfs2/ops_fstype.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
> index c0cf1d2d0ef5..934746f18c25 100644
> --- a/fs/gfs2/ops_fstype.c
> +++ b/fs/gfs2/ops_fstype.c
> @@ -1446,12 +1446,18 @@ static int gfs2_parse_param(struct fs_context *fc, struct fs_parameter *param)
>
>         switch (o) {
>         case Opt_lockproto:
> +               if (!param->string)
> +                       goto bad_val;
>                 strscpy(args->ar_lockproto, param->string, GFS2_LOCKNAME_LEN);
>                 break;
>         case Opt_locktable:
> +               if (!param->string)
> +                       goto bad_val;
>                 strscpy(args->ar_locktable, param->string, GFS2_LOCKNAME_LEN);
>                 break;
>         case Opt_hostdata:
> +               if (!param->string)
> +                       goto bad_val;
>                 strscpy(args->ar_hostdata, param->string, GFS2_LOCKNAME_LEN);
>                 break;
>         case Opt_spectator:
> @@ -1535,6 +1541,10 @@ static int gfs2_parse_param(struct fs_context *fc, struct fs_parameter *param)
>                 return invalfc(fc, "invalid mount option: %s", param->key);
>         }
>         return 0;
> +
> +bad_val:
> +       return invalfc(fc, "Bad value '%s' for mount option '%s'\n",
> +                      param->string, param->key);
>  }
>
>  static int gfs2_reconfigure(struct fs_context *fc)
> --
> 2.25.1
>

Thanks,
Andreas