[gnutls-devel] GnuTLS | GnuTLS leaks file descriptors in child processes (#985)

[Development of GNU's TLS library]

Remi Denis-Courmont commented:


I doubt that. Normally you need the flag to be set atomically in multi-thread context. That's the whole point of using *_CLOEXEC flags.

Otherwise there is a race if a thread calls `fork()` between the `fopen()` and the `set_close_exec()` flag. `fork()` copies the flag at the time of forking.

For instance:

* Thread A calls `gnutls_handshake()`... which opens the master key log file wit `fopen()`.
  * This creates a new file descriptor (without close-on-exec flag).
* Thread B calls `fork()` from application code.
  * The file descriptor is copied into the child process (also without the close-on-exec flag).
* Thread A calls `set_cloese_exec()` (or directly `fcntl()`).
  * This sets the flag on the parent process FD, but not the child process FD.
* Child process calls `execv()` oblivious to the FD. The master key log FD is leaked to the child process.

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