The functions grub_util_exec_pipe() and grub_util_exec_pipe_stderr()
currently call execvp(). If the call fails for any reason, the child
currently calls exit(127). This in turn executes the parents
atexit() handlers from the forked child, and then the same handlers
are called again from parent. This is usually not desired, and can
lead to deadlocks, and undesired behavior. So, change the exit() calls
to _exit() calls to avoid calling atexit() handlers from child.
Fixes: e75cf4a58 (unix exec: avoid atexit handlers when child exits)
Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Bug-Debian: https://bugs.debian.org/983435
Last-Update: 2021-06-14
Patch-Name: osdep-exec-avoid-atexit-when-child-exits.patch
The `grub_util_exec_redirect_all` helper function can be used to
spawn an executable and redirect its output to some files. After calling
`fork()`, the parent will wait for the child to terminate with
`waitpid()` while the child prepares its file descriptors, environment
and finally calls `execvp()`. If something in the children's setup
fails, it will stop by calling `exit(127)`.
Calling `exit()` will cause any function registered via `atexit()` to be
executed, which is usually the wrong thing to do in a child. And
actually, one can easily observe faulty behaviour on musl-based systems
without modprobe(8) installed: executing `grub-install --help` will call
`grub_util_exec_redirect_all` with "modprobe", which obviously fails if
modprobe(8) is not installed. Due to the child now exiting and invoking
the `atexit()` handlers, it will clean up some data structures of the
parent and cause it to be deadlocked in the `waitpid()` syscall.
The issue can easily be fixed by calling `_exit(127)` instead, which is
especially designed to be called when the atexit-handlers should not be
executed.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
We need to hide "modprobe efivars" error output to avoid confusion. So
consolidate grub_util_exec_* into single function that can optionally redirect
all three standard descriptors and make all other functions compatibility
wrappers.
Also remove include/grub/osdep/exec_unix.h which does not appear to be used
anywhere.
references to mdadm from otherwise generic code.
(grub_util_exec_pipe): Likewise.
(grub_util_exec_pipe_stderr): Likewise.
* grub-core/osdep/unix/getroot.c (grub_util_pull_lvm_by_command):
This function calls vgs, not mdadm; adjust variable names
accordingly.
the function of these files exceeds what can be sanely handled in shell
in posix-comaptible way. Also writing it in C extends the functionality
to non-UNIX-like OS and minimal environments.
