Rollup merge of rust-lang#62425 - cyphar:linux-cloexec-use-fcntl, r=a…

…lexcrichton

filedesc: don't use ioctl(FIOCLEX) on Linux

All `ioctl(2)`s will fail on `O_PATH` file descriptors on Linux (because
they use `&empty_fops` as a security measure against `O_PATH` descriptors
affecting the backing file).

As a result, `File::try_clone()` and various other methods would always
fail with `-EBADF` on `O_PATH` file descriptors. The solution is to simply
use `F_SETFD` (as is used on other unices) which works on `O_PATH`
descriptors because it operates through the `fnctl(2)` layer and not
through `ioctl(2)`s.

Since this code is usually only used in strange error paths (a broken or
ancient kernel), the extra overhead of one syscall shouldn't cause any
dramas. Most other systems programming languages also use the fnctl(2)
so this brings us in line with them.

Fixes: rust-lang#62314
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

src/libstd/sys/unix/fd.rs

@@ -175,6 +175,7 @@ impl FileDesc {
                   target_os = "emscripten",
                   target_os = "fuchsia",
                   target_os = "l4re",
+                  target_os = "linux",
                   target_os = "haiku")))]
     pub fn set_cloexec(&self) -> io::Result<()> {
         unsafe {
@@ -187,6 +188,7 @@ impl FileDesc {
               target_os = "emscripten",
               target_os = "fuchsia",
               target_os = "l4re",
+              target_os = "linux",
               target_os = "haiku"))]
     pub fn set_cloexec(&self) -> io::Result<()> {
         unsafe {