In the Linux kernel, the following vulnerability has been resolved:
exec: do_close_on_exec() before taking exec_update_lock
do_close_on_exec() currently happens while holding the exec_update_lock,
which is used in a lot of places that access process state to
synchronize access checks.
I recently added another such use of exec_update_lock, causing a
regression.
do_close_on_exec() can block waiting for a reply from a filesystem.
That means a hung filesystem can block codepaths that use
exec_update_lock; and it also means that a FUSE filesystem which
attempts to inspect the calling process can deadlock.
To avoid such problems, move do_close_on_exec() before the
exec_update_lock is taken, but after the FD table has been copied if
necessary.
I have looked through all the calls between the old and new position of
the do_close_on_exec() call; there seems to be no file descriptor table
access in between.
