vfs_default: allow disabling /proc/fds and RESOLVE_NO_SYMLINK at compile time

This will be used in CI to have a gitlab runner without all modern Linux
features we make use of as part of path processing:

- O_PATH
- openat2() with RESOLVE_NO_SYMLINKS
- somehow safely reopen an O_PATH file handle

That gives what a classix UNIX like AIX or Solaris offers feature wise.

Other OSes support other combinations of those features, but we leave the
exersize of possibly adding more runners supporting those combinations to the
reader.

The following list shows which features are available and used by Samba on a few
OSes:

        | O_PATH         | RESOLVE_NO_SYMLINKS | Safe reopen    | CI covered
--------|----------------|---------------------|----------------------------
        | Supported Used | Supported Used      | Supported Used |
============================================================================
Linux   | +         +    | +         +         | +         +    | +
FreeBSD | +         +    | + [1]     -         | + [2]     -    | -
AIX     | -         -    | -         -         | -         -    | +

[1] via open() flag O_RESOLVE_BENEATH
[2] via open() flag O_EMPTY_PATH

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15549

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
(cherry picked from commit 5c2f96442a25a1725809a28b3719afbc0bd01830)

diff --git a/source3/modules/vfs_default.c b/source3/modules/vfs_default.c
index 1d4b9b1a8402f056d26153f50d5aecd59b2df401..8d78831492f05ec36e8d3a46f5684cb58b027eaf 100644 (file)
--- a/source3/modules/vfs_default.c
+++ b/source3/modules/vfs_default.c
@@ -52,6 +52,9 @@ static int vfswrap_connect(vfs_handle_struct *handle, const char *service, const
        bool bval;
 
        handle->conn->have_proc_fds = sys_have_proc_fds();
+#ifdef DISABLE_PROC_FDS
+       handle->conn->have_proc_fds = false;
+#endif
 
        /*
         * assume the kernel will support openat2(),
@@ -70,6 +73,9 @@ static int vfswrap_connect(vfs_handle_struct *handle, const char *service, const
                handle->conn->open_how_resolve |=
                        VFS_OPEN_HOW_RESOLVE_NO_SYMLINKS;
        }
+#ifdef DISABLE_VFS_OPEN_HOW_RESOLVE_NO_SYMLINKS
+       handle->conn->open_how_resolve &= ~VFS_OPEN_HOW_RESOLVE_NO_SYMLINKS;
+#endif
 
        return 0;    /* Return >= 0 for success */
 }