Re: [PATCH v2 2/5] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS

[Akihiko Odaki <akihiko.odaki@gmail.com>]

On 2022/04/22 0:07, Christian Schoenebeck wrote:
> mknod() on macOS does not support creating sockets, so divert to
> call sequence socket(), bind() and chmod() respectively if S_IFSOCK
> was passed with mode argument.
> 
> Link: https://lore.kernel.org/qemu-devel/17933734.zYzKuhC07K@silver/
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> Reviewed-by: Will Cohen <wwcohen@gmail.com>
> ---
>   hw/9pfs/9p-util-darwin.c | 27 ++++++++++++++++++++++++++-
>   1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
> index e24d09763a..39308f2a45 100644
> --- a/hw/9pfs/9p-util-darwin.c
> +++ b/hw/9pfs/9p-util-darwin.c
> @@ -74,6 +74,27 @@ int fsetxattrat_nofollow(int dirfd, const char *filename, const char *name,
>    */
>   #if defined CONFIG_PTHREAD_FCHDIR_NP
>   
> +static int create_socket_file_at_cwd(const char *filename, mode_t mode) {
> +    int fd, err;
> +    struct sockaddr_un addr = {
> +        .sun_family = AF_UNIX
> +    };
> +
> +    fd = socket(PF_UNIX, SOCK_DGRAM, 0);
> +    if (fd == -1) {
> +        return fd;
> +    }
> +    snprintf(addr.sun_path, sizeof(addr.sun_path), "./%s", filename);

It would result in an incorrect path if the path does not fit in 
addr.sun_path. It should report an explicit error instead.

> +    err = bind(fd, (struct sockaddr *) &addr, sizeof(addr));
> +    if (err == -1) {
> +        goto out;

You may close(fd) as soon as bind() returns (before checking the 
returned value) and eliminate goto.

> +    }
> +    err = chmod(addr.sun_path, mode);

I'm not sure if it is fine to have a time window between bind() and 
chmod(). Do you have some rationale?

Regards,
Akihiko Odaki

> +out:
> +    close(fd);
> +    return err;
> +}
> +
>   int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
>   {
>       int preserved_errno, err;
> @@ -93,7 +114,11 @@ int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
>       if (pthread_fchdir_np(dirfd) < 0) {
>           return -1;
>       }
> -    err = mknod(filename, mode, dev);
> +    if (S_ISSOCK(mode)) {
> +        err = create_socket_file_at_cwd(filename, mode);
> +    } else {
> +        err = mknod(filename, mode, dev);
> +    }
>       preserved_errno = errno;
>       /* Stop using the thread-local cwd */
>       pthread_fchdir_np(-1);