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Re: [PATCH v4 2/6] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS
From: |
Christian Schoenebeck |
Subject: |
Re: [PATCH v4 2/6] 9pfs: fix qemu_mknodat(S_IFSOCK) on macOS |
Date: |
Thu, 28 Apr 2022 13:22:26 +0200 |
On Mittwoch, 27. April 2022 22:36:25 CEST Greg Kurz wrote:
> On Wed, 27 Apr 2022 20:54:17 +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 | 45 +++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 44 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/9pfs/9p-util-darwin.c b/hw/9pfs/9p-util-darwin.c
> > index e24d09763a..7d00db47a9 100644
> > --- a/hw/9pfs/9p-util-darwin.c
> > +++ b/hw/9pfs/9p-util-darwin.c
> > @@ -74,6 +74,45 @@ 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
> > + };
> > +
> > + /*
> > + * sun_path is only 104 bytes, explicit filename length check
> > required
> > + */
> > + if (sizeof(addr.sun_path) - 1 < strlen(filename) + 2) {
>
> True but I was a bit puzzled by the math until I realized the '+ 2' was
> for the prepended "./" ;-)
Correct ...
> > + errno = ENAMETOOLONG;
> > + return -1;
> > + }
> > + fd = socket(PF_UNIX, SOCK_DGRAM, 0);
> > + if (fd == -1) {
> > + return fd;
> > + }
> > + snprintf(addr.sun_path, sizeof(addr.sun_path), "./%s", filename);
>
> What about the more generic approach of checking snprintf()'s return
> value ? If it is >= sizeof(addr.sun_path) then truncation occured.
... well, I can send a v5 if you prefer that solution, or you can send a
follow-up
patch later on. As you wish.
> > + 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);
>
> You could close(fd) earlier now, but you might want to keep the code
> as is in case FB9997731 gets proper attention.
>
> Anyway, this should do the job so:
Sounds like Akihiko's previous suggestion. I would keep it that way:
eafd4bbf-dbff-323a-179f-8f29905701e1@gmail.com/">https://lore.kernel.org/qemu-devel/eafd4bbf-dbff-323a-179f-8f29905701e1@gmail.com/
> Reviewed-by: Greg Kurz <groug@kaod.org>
Thanks!
Best regards,
Christian Schoenebeck
> > + return err;
> > +}
> > +
> >
> > int qemu_mknodat(int dirfd, const char *filename, mode_t mode, dev_t dev)
> > {
> >
> > int preserved_errno, err;
> >
> > @@ -93,7 +132,11 @@ 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 v4 0/6] 9pfs: macOS host fixes, Christian Schoenebeck, 2022/04/27
- [PATCH v4 3/6] 9pfs: fix wrong encoding of rdev field in Rgetattr on macOS, Christian Schoenebeck, 2022/04/27
- [PATCH v4 4/6] 9pfs: fix wrong errno being sent to Linux client on macOS host, Christian Schoenebeck, 2022/04/27
- [PATCH v4 5/6] 9pfs: fix removing non-existent POSIX ACL xattr on macOS host, Christian Schoenebeck, 2022/04/27
- [PATCH v4 6/6] 9pfs: fix qemu_mknodat() to always return -1 on error on macOS host, Christian Schoenebeck, 2022/04/27