smbd: optimisation using pathref fd to open real fd if possible

This is an optimisation that avoids going through the expensive
non_widelink_open() logic a second time. It depends on a usable /proc/%d/fd/%d
filesystem and this is checked and set as "can_reopen" flag by the VFS in the
openat() function in the fsp.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

diff --git a/source3/smbd/open.c b/source3/smbd/open.c
index 106d827dcc94023484e5f58429de6ddd78c89c38..857643ddacfaa6da478c03d878586fa153133110 100644 (file)
--- a/source3/smbd/open.c
+++ b/source3/smbd/open.c
@@ -1188,6 +1188,71 @@ static NTSTATUS fd_open_atomic(files_struct *fsp,
        return status;
 }
 
+static NTSTATUS reopen_from_procfd(struct files_struct *fsp,
+                                  struct smb_filename *smb_fname,
+                                  int flags,
+                                  mode_t mode)
+{
+       struct smb_filename proc_fname;
+       const char *p = NULL;
+       char buf[PATH_MAX];
+       int old_fd;
+       int new_fd;
+       NTSTATUS status;
+       int ret;
+
+       if (!fsp->fsp_flags.have_proc_fds) {
+               return NT_STATUS_MORE_PROCESSING_REQUIRED;
+       }
+
+       old_fd = fsp_get_pathref_fd(fsp);
+       if (old_fd == -1) {
+               return NT_STATUS_MORE_PROCESSING_REQUIRED;
+       }
+
+       if (!fsp->fsp_flags.is_pathref) {
+               DBG_ERR("[%s] is not a pathref\n",
+                       smb_fname_str_dbg(smb_fname));
+#ifdef DEVELOPER
+               smb_panic("Not a pathref");
+#endif
+               return NT_STATUS_INVALID_HANDLE;
+       }
+
+       p = sys_proc_fd_path(old_fd, buf, sizeof(buf));
+       if (p == NULL) {
+               return NT_STATUS_NO_MEMORY;
+       }
+
+       proc_fname = (struct smb_filename) {
+               .base_name = discard_const_p(char, p),
+       };
+
+       fsp->fsp_flags.is_pathref = false;
+
+       new_fd = SMB_VFS_OPENAT(fsp->conn,
+                               fsp->conn->cwd_fsp,
+                               &proc_fname,
+                               fsp,
+                               flags,
+                               mode);
+       if (new_fd == -1) {
+               status = map_nt_error_from_unix(errno);
+               SMB_VFS_CLOSE(fsp);
+               fsp_set_fd(fsp, -1);
+               return status;
+       }
+
+       ret = SMB_VFS_CLOSE(fsp);
+       fsp_set_fd(fsp, -1);
+       if (ret != 0) {
+               return map_nt_error_from_unix(errno);
+       }
+
+       fsp_set_fd(fsp, new_fd);
+       return NT_STATUS_OK;
+}
+
 /****************************************************************************
  Open a file.
 ****************************************************************************/
@@ -1366,24 +1431,33 @@ static NTSTATUS open_file(files_struct *fsp,
                        }
                }
 
-               /*
-                * Close the existing pathref fd and set fsp_flags.is_pathref to
-                * false so we get a full fd this time.
-                */
-               status = fd_close(fsp);
-               if (!NT_STATUS_IS_OK(status)) {
-                       return status;
-               }
-               fsp->fsp_flags.is_pathref = false;
-
                /*
                 * Actually do the open - if O_TRUNC is needed handle it
                 * below under the share mode lock.
                 */
-               status = fd_open_atomic(fsp,
-                                       local_flags & ~O_TRUNC,
-                                       unx_mode,
-                                       p_file_created);
+               status = reopen_from_procfd(fsp,
+                                           smb_fname,
+                                           local_flags & ~O_TRUNC,
+                                           unx_mode);
+               if (NT_STATUS_EQUAL(status, NT_STATUS_MORE_PROCESSING_REQUIRED))
+               {
+                       /*
+                        * Close the existing pathref fd and set the fsp flag
+                        * is_pathref to false so we get a "normal" fd this
+                        * time.
+                        */
+                       status = fd_close(fsp);
+                       if (!NT_STATUS_IS_OK(status)) {
+                               return status;
+                       }
+
+                       fsp->fsp_flags.is_pathref = false;
+
+                       status = fd_open_atomic(fsp,
+                                               local_flags & ~O_TRUNC,
+                                               unx_mode,
+                                               p_file_created);
+               }
                if (NT_STATUS_EQUAL(status, NT_STATUS_STOPPED_ON_SYMLINK)) {
                        /*
                         * POSIX client that hit a symlink. We don't want to
@@ -4562,28 +4636,32 @@ static NTSTATUS open_directory(connection_struct *conn,
        */
        mtimespec = make_omit_timespec();
 
-       /*
-        * Close the existing pathref fd and set fsp_flags.is_pathref to
-        * false so we get a full fd this time.
-        */
-       status = fd_close(fsp);
-       if (!NT_STATUS_IS_OK(status)) {
-               return status;
-       }
-       fsp->fsp_flags.is_pathref = false;
-
        /* POSIX allows us to open a directory with O_RDONLY. */
        flags = O_RDONLY;
 #ifdef O_DIRECTORY
        flags |= O_DIRECTORY;
 #endif
 
-       status = fd_openat(conn->cwd_fsp, fsp->fsp_name, fsp, flags, 0);
+       status = reopen_from_procfd(fsp, smb_dname, flags, 0);
+       if (NT_STATUS_EQUAL(status, NT_STATUS_MORE_PROCESSING_REQUIRED)) {
+               /*
+                * Close the existing pathref fd and set the fsp flag
+                * is_pathref to false so we get a "normal" fd this
+                * time.
+                */
+               status = fd_close(fsp);
+               if (!NT_STATUS_IS_OK(status)) {
+                       return status;
+               }
+
+               fsp->fsp_flags.is_pathref = false;
+
+               status = fd_openat(conn->cwd_fsp, fsp->fsp_name, fsp, flags, 0);
+       }
        if (!NT_STATUS_IS_OK(status)) {
-               DBG_INFO("Could not open fd for "
-                       "%s (%s)\n",
-                       smb_fname_str_dbg(smb_dname),
-                       nt_errstr(status));
+               DBG_INFO("Could not open fd for%s (%s)\n",
+                        smb_fname_str_dbg(smb_dname),
+                        nt_errstr(status));
                return status;
        }