ima: eliminate passing d_name.name to process_measurement()

Passing a pointer to the dentry name, as a parameter to
process_measurement(), causes a race condition with rename() and
is unnecessary, as the dentry name is already accessible via the
file parameter.

In the normal case, we use the full pathname as provided by
brpm->filename, bprm->interp, or ima_d_path(). Only on ima_d_path()
failure, do we fallback to using the d_name.name, which points
either to external memory or d_iname.

Reported-by: Al Viro <[e-mail]>
Signed-off-by: Mimi Zohar <[e-mail]>
Signed-off-by: James Morris <[e-mail]>

security/integrity/ima/ima_main.c

···
 	if (rc != 0)
 		goto out_digsig;
 
-	if (function != BPRM_CHECK)
-		pathname = ima_d_path(&file->f_path, &pathbuf);
-
+	pathname = !filename ? ima_d_path(&file->f_path, &pathbuf) : filename;
 	if (!pathname)
-		pathname = filename;
+		pathname = (const char *)file->f_dentry->d_name.name;
 
 	if (action & IMA_MEASURE)
 		ima_store_measurement(iint, file, pathname);
···
 int ima_file_mmap(struct file *file, unsigned long prot)
 {
 	if (file && (prot & PROT_EXEC))
-		return process_measurement(file, file->f_dentry->d_name.name,
-					   MAY_EXEC, MMAP_CHECK);
+		return process_measurement(file, NULL, MAY_EXEC, MMAP_CHECK);
 	return 0;
 }
 
···
 int ima_file_check(struct file *file, int mask)
 {
 	ima_rdwr_violation_check(file);
-	return process_measurement(file, file->f_dentry->d_name.name,
+	return process_measurement(file, NULL,
 				 mask & (MAY_READ | MAY_WRITE | MAY_EXEC),
 				 FILE_CHECK);
 }
···
 #endif
 		return 0;	/* We rely on module signature checking */
 	}
-	return process_measurement(file, file->f_dentry->d_name.name,
-				   MAY_EXEC, MODULE_CHECK);
+	return process_measurement(file, NULL, MAY_EXEC, MODULE_CHECK);
 }
 
 static int __init init_ima(void)