Merged PR 692773: Properly invalidate the file descriptor table on fork/clone

Some other cases where we were not doing the proper file descriptor cache invalidation:
* Fork/clone: the entire fd table needs to be invalidated for the child process since fd are local to a process
* Internal open handles (sandbox sending reports/logging) also need to clean up their corresponding entries as a defense for missing close(fd),

Author: smera

Public/Src/Sandbox/Linux/bxl_observer.cpp

@@ -203,7 +203,13 @@ bool BxlObserver::Send(const char *buf, size_t bufsiz)
         _fatal("Wrote only %ld bytes out of %ld", numWritten, bufsiz);
     }
 
+    // A handle was opened for our own internal purposes. That
+    // could have reused a fd where we missed a close, 
+    // so reset that entry in the fd table
+    reset_fd_table_entry(logFd);
+
     real_close(logFd);
+
     return true;
 }
 
@@ -376,6 +382,14 @@ void BxlObserver::reset_fd_table_entry(int fd)
     }
 }
 
+void BxlObserver::reset_fd_table()
+{
+    for (int i = 0; i < MAX_FD; i++)
+    {
+        fdTable_[i] = empty_str_;
+    }
+}
+
 std::string BxlObserver::fd_to_path(int fd)
 {
     char path[PATH_MAX] = {0};

Public/Src/Sandbox/Linux/bxl_observer.hpp

@@ -298,7 +298,10 @@ class BxlObserver final
     // and the write is allowed by policy
     AccessCheckResult report_firstAllowWriteCheck(const char *fullPath);
 
+    // Clears the specified entry on the file descriptor table
     void reset_fd_table_entry(int fd);
+    // Clears the entire file descriptor table
+    void reset_fd_table();
     std::string fd_to_path(int fd);
     std::string normalize_path_at(int dirfd, const char *pathname, int oflags = 0);
 
@@ -321,6 +324,12 @@ class BxlObserver final
                 va_start(args, fmt);
                 real_vfprintf(f, fmt, args);
                 va_end(args);
+
+                // A handle was opened for our own internal purposes. That
+                // could have reused a fd where we missed a close, 
+                // so reset that entry in the fd table
+                reset_fd_table_entry(fileno(f));
+
                 real_fclose(f);
             }
         }

Public/Src/Sandbox/Linux/detours.cpp

@@ -53,9 +53,15 @@ static int ret_fd(int fd, BxlObserver *bxl)
 INTERPOSE(pid_t, fork, void)({
     result_t<pid_t> childPid = bxl->fwd_fork();
 
-    // report fork only when we are in the parent process
-    if (childPid.get() > 0)
+    if (childPid.get() == 0)
     {
+        // Clear the file descriptor table when we are in the child process
+        // File descriptors are unique to a process, so this cache needs to be invalidated on the child
+        bxl->reset_fd_table();
+    }
+    else
+    {
+        // report fork only when we are in the parent process
         report_child_process(__func__, bxl, childPid.get());
     }
 
@@ -71,8 +77,16 @@ INTERPOSE(int, clone, int (*fn)(void *), void *child_stack, int flags, void *arg
     va_end(args);
 
     result_t<int> result = bxl->fwd_clone(fn, child_stack, flags, arg, ptid, newtls, ctid);
-    if (result.get() > 0)
+    
+    if (result.get() == 0)
+    {
+        // Clear the file descriptor table when we are in the child process
+        // File descriptors are unique to a process, so this cache needs to be invalidated on the child
+        bxl->reset_fd_table();
+    }
+    else
     {
+        // report clone only when we are in the parent process
         report_child_process(__func__, bxl, result.get());
     }