Re: [Qemu-devel] [PATCH] file-posix: refuse to open directories

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Dec 21, 2017 at 05:44:11PM -0500, John Snow wrote:
> I don't think there's a legitimate reason to open directories as if
> they were files. This prevents QEMU from opening and attempting to probe
> a directory inode, which can break in exciting ways. One of those ways
> is lseek on ext4/xfs, which will return 0x7fffffffffffffff as the file
> size instead of EISDIR. This can coax QEMU into responding with a
> confusing "file too big" instead of "Hey, that's not a file".
> 
> See: https://bugs.launchpad.net/qemu/+bug/1739304/
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  block/file-posix.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 36ee89e940..bd29bdada6 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -589,6 +589,11 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
>          s->needs_alignment = true;
>      }
>  #endif
> +    if (S_ISDIR(st.st_mode)) {
> +        ret = -EISDIR;
> +        error_setg_errno(errp, errno, "Cannot open directory as file");
> +        goto fail;
> +    }

Should we also do the same for S_ISCHR & S_ISFIFO, because neither of
them allow seeking, which IIUC would prevent usage in the file driver
for random I/O.  It would be fine todo that in a followup patch though,
so from this patch pov

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>


Regards,
Daniel
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