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author | Tavian Barnes <tavianator@tavianator.com> | 2021-02-20 16:21:42 -0500 |
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committer | Tavian Barnes <tavianator@tavianator.com> | 2021-02-20 19:06:08 -0500 |
commit | c6c851403b6bd16c93227c309abad3e95f5476bf (patch) | |
tree | 8de9235ff4da569cd4821ff37ef81ab9839fca5e /src/pty.rs | |
parent | d0bba22db495951d4488e615f35c8d9c87eb1ff2 (diff) | |
download | nix-c6c851403b6bd16c93227c309abad3e95f5476bf.zip |
pty: Make forkpty() unsafe
After the child returns from a fork() of a multi-threaded process, it is
undefined behaviour to call non-async-signal-safe functions according to
POSIX. Since forkpty() is implemented in terms of fork(), those
restrictions should apply to it too.
Diffstat (limited to 'src/pty.rs')
-rw-r--r-- | src/pty.rs | 29 |
1 files changed, 18 insertions, 11 deletions
@@ -302,7 +302,19 @@ pub fn openpty<'a, 'b, T: Into<Option<&'a Winsize>>, U: Into<Option<&'b Termios> /// If `winsize` is not `None`, the window size of the slave will be set to /// the values in `winsize`. If `termios` is not `None`, the pseudoterminal's /// terminal settings of the slave will be set to the values in `termios`. -pub fn forkpty<'a, 'b, T: Into<Option<&'a Winsize>>, U: Into<Option<&'b Termios>>>( +/// +/// # Safety +/// +/// In a multithreaded program, only [async-signal-safe] functions like `pause` +/// and `_exit` may be called by the child (the parent isn't restricted). Note +/// that memory allocation may **not** be async-signal-safe and thus must be +/// prevented. +/// +/// Those functions are only a small subset of your operating system's API, so +/// special care must be taken to only invoke code you can control and audit. +/// +/// [async-signal-safe]: http://man7.org/linux/man-pages/man7/signal-safety.7.html +pub unsafe fn forkpty<'a, 'b, T: Into<Option<&'a Winsize>>, U: Into<Option<&'b Termios>>>( winsize: T, termios: U, ) -> Result<ForkptyResult> { @@ -323,20 +335,15 @@ pub fn forkpty<'a, 'b, T: Into<Option<&'a Winsize>>, U: Into<Option<&'b Termios> .map(|ws| ws as *const Winsize as *mut _) .unwrap_or(ptr::null_mut()); - let res = unsafe { - libc::forkpty(master.as_mut_ptr(), ptr::null_mut(), term, win) - }; + let res = libc::forkpty(master.as_mut_ptr(), ptr::null_mut(), term, win); let fork_result = Errno::result(res).map(|res| match res { 0 => ForkResult::Child, res => ForkResult::Parent { child: Pid::from_raw(res) }, })?; - unsafe { - Ok(ForkptyResult { - master: master.assume_init(), - fork_result, - }) - } + Ok(ForkptyResult { + master: master.assume_init(), + fork_result, + }) } - |