[Samba] O_PATH, FreeBSD & acl_xx_fd

[Jeremy Allison]

On Tue, May 30, 2023 at 07:40:41PM +0200, Peter Eriksson via samba wrote:
>Urgh…
>
>I modified the FreeBSD kernel to allow all_xx_fd() calls on O_PATH descriptors and that seems make vfs_zfsacl to work fine. Not 100% tested but I could atleast view and modify the ACL on some stuff from a Windows client via Samba that way.
>
>I’m not sure I’ll be able to get them to implement this “officially” though. Reading ACLs via an O_PATH-opened descriptor seems to be on the way of being added though. I can always use my custom kernel but… :-)
>
>Regarding that Linux hack - I wonder if on FreeBSD one might use this to do something similar:
>
>>   A file descriptor created with the O_PATH flag can be opened into normal
>>     (operable) file descriptor by specifying it as the fd argument to
>>     openat() with empty path and flag O_EMPTY_PATH.  Such an open behaves as
>>     if the current path of the file referenced by fd is passed, except that
>>     the path walk permissions are not checked.  See also the description of
>>     AT_EMPTY_PATH flag for fstatat(2) and related syscalls.
>
>Hmm… I’ll have to test it. Yes, this seems to work - after this I can read & write ACLs and stuff:
>
>   fd = openat(fd, “”, O_EMPTY_PATH);

Excellent ! These are the current places where the
horrid hack is used:

git grep sys_proc_fd_path
source3/include/proto.h:const char *sys_proc_fd_path(int fd, char *buf, size_t bufsize);
source3/lib/system.c:const char *sys_proc_fd_path(int fd, char *buf, size_t bufsize)
source3/modules/vfs_btrfs.c:    p = sys_proc_fd_path(fsp_fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_default.c:          p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_gpfs.c:                     p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_gpfs.c:             p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_gpfs.c:             p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_gpfs.c:             p = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_posixacl.c:         proc_fd_path = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_posixacl.c:         proc_fd_path = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/modules/vfs_posixacl.c:         proc_fd_path = sys_proc_fd_path(fd, buf, sizeof(buf));
source3/smbd/open.c:    p = sys_proc_fd_path(old_fd, buf, sizeof(buf));

So these are all the places you're going to run into the
same problem with O_PATH opened fd's.

FYI, this really belongs on samba-technical, not samba.