vfs: Don't ever call openat(-1, ...) for relative paths

This is always a bug, we should never do this. In one iteration of my
code I was doing this, which led to an invalid fallback code, which
itself lead to an infinite recursion. Make this more obvious with an
assert.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue Nov 12 15:13:03 UTC 2024 on atb-devel-224

diff --git a/source3/modules/vfs_default.c b/source3/modules/vfs_default.c
index e895de189fae0b556b3348b171fe37515f1527fe..f4032656e1f5fc1745209e9bfc454aaaaa35bf17 100644 (file)
--- a/source3/modules/vfs_default.c
+++ b/source3/modules/vfs_default.c
@@ -607,6 +607,7 @@ static int vfswrap_openat(vfs_handle_struct *handle,
                          files_struct *fsp,
                          const struct vfs_open_how *how)
 {
+       int dirfd = fsp_get_pathref_fd(dirfsp);
        int flags = how->flags;
        mode_t mode = how->mode;
        bool have_opath = false;
@@ -615,6 +616,8 @@ static int vfswrap_openat(vfs_handle_struct *handle,
 
        START_PROFILE(syscall_openat);
 
+       SMB_ASSERT((dirfd != -1) || (smb_fname->base_name[0] == '/'));
+
        if (how->resolve & ~(VFS_OPEN_HOW_RESOLVE_NO_SYMLINKS |
                             VFS_OPEN_HOW_WITH_BACKUP_INTENT)) {
                errno = ENOSYS;
@@ -656,7 +659,7 @@ static int vfswrap_openat(vfs_handle_struct *handle,
                        .resolve = RESOLVE_NO_SYMLINKS,
                };
 
-               result = openat2(fsp_get_pathref_fd(dirfsp),
+               result = openat2(dirfd,
                                 smb_fname->base_name,
                                 &linux_how,
                                 sizeof(linux_how));
@@ -683,7 +686,7 @@ static int vfswrap_openat(vfs_handle_struct *handle,
                became_root = true;
        }
 
-       result = openat(fsp_get_pathref_fd(dirfsp),
+       result = openat(dirfd,
                        smb_fname->base_name,
                        flags,
                        mode);