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

[Akihiko Odaki]

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_...@crudebyte.com>
Reviewed-by: Will Cohen <wwco...@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);