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Re: [PATCH v5 2/6] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS
From: |
Greg Kurz |
Subject: |
Re: [PATCH v5 2/6] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS |
Date: |
Fri, 29 Apr 2022 14:56:50 +0200 |
On Fri, 29 Apr 2022 12:25:11 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:
> mknod() on macOS does not support creating sockets, so divert to
> call sequence socket(), bind() and fchmodat() 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>
> ---
> hw/9pfs/9p-util-darwin.c | 42 +++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
> index e24d09763a..619c403ba7 100644
> --- a/hw/9pfs/9p-util-darwin.c
> +++ b/hw/9pfs/9p-util-darwin.c
> @@ -74,6 +74,42 @@ 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
> + };
> +
> + err = snprintf(addr.sun_path, sizeof(addr.sun_path), "./%s", filename);
> + if (err < 0 || err >= sizeof(addr.sun_path)) {
According to POSIX [1]:
The snprintf() function shall fail if:
[EOVERFLOW]
[CX] [Option Start] The value of n is greater than {INT_MAX}. [Option End]
[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html
Since we're passing sizeof(addr.sun_path), I'm pretty sure snprintf()
cannot fail. No big deal.
Reviewed-by: Greg Kurz <groug@kaod.org>
> + errno = ENAMETOOLONG;
> + return -1;
> + }
> + fd = socket(PF_UNIX, SOCK_DGRAM, 0);
> + if (fd == -1) {
> + return fd;
> + }
> + err = bind(fd, (struct sockaddr *) &addr, sizeof(addr));
> + if (err == -1) {
> + goto out;
> + }
> + /*
> + * FIXME: Should rather be using descriptor-based fchmod() on the
> + * socket file descriptor above (preferably before bind() call),
> + * instead of path-based fchmodat(), to prevent concurrent transient
> + * state issues between creating the named FIFO file at bind() and
> + * delayed adjustment of permissions at fchmodat(). However currently
> + * macOS (12.x) does not support such operations on socket file
> + * descriptors yet.
> + *
> + * Filed report with Apple: FB9997731
> + */
> + err = fchmodat(AT_FDCWD, filename, mode, AT_SYMLINK_NOFOLLOW_ANY);
> +out:
> + close_preserve_errno(fd);
> + return err;
> +}
> +
> int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
> {
> int preserved_errno, err;
> @@ -93,7 +129,11 @@ 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);
[PATCH v5 3/6] 9pfs: fix wrong encoding of rdev field in Rgetattr on macOS, Christian Schoenebeck, 2022/04/29
[PATCH v5 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Christian Schoenebeck, 2022/04/29