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unix exec: avoid atexit handlers when child exits

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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>
This commit is contained in:
Patrick Steinhardt 2017-08-28 20:57:19 +02:00 committed by Vladimir Serbinenko
parent 3d86efda00
commit e75cf4a58b
1 changed files with 4 additions and 4 deletions
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8
grub-core/osdep/unix/exec.c
View file

@ -99,7 +99,7 @@ grub_util_exec_redirect_all (const char *const *argv, const char *stdin_file,
{ {
fd = open (stdin_file, O_RDONLY); fd = open (stdin_file, O_RDONLY);
if (fd < 0) if (fd < 0)
exit (127); _exit (127);
dup2 (fd, STDIN_FILENO); dup2 (fd, STDIN_FILENO);
close (fd); close (fd);
} }
@ -108,7 +108,7 @@ grub_util_exec_redirect_all (const char *const *argv, const char *stdin_file,
{ {
fd = open (stdout_file, O_WRONLY | O_CREAT, 0700); fd = open (stdout_file, O_WRONLY | O_CREAT, 0700);
if (fd < 0) if (fd < 0)
exit (127); _exit (127);
dup2 (fd, STDOUT_FILENO); dup2 (fd, STDOUT_FILENO);
close (fd); close (fd);
} }
@ -117,7 +117,7 @@ grub_util_exec_redirect_all (const char *const *argv, const char *stdin_file,
{ {
fd = open (stderr_file, O_WRONLY | O_CREAT, 0700); fd = open (stderr_file, O_WRONLY | O_CREAT, 0700);
if (fd < 0) if (fd < 0)
exit (127); _exit (127);
dup2 (fd, STDERR_FILENO); dup2 (fd, STDERR_FILENO);
close (fd); close (fd);
} }
@ -126,7 +126,7 @@ grub_util_exec_redirect_all (const char *const *argv, const char *stdin_file,
setenv ("LC_ALL", "C", 1); setenv ("LC_ALL", "C", 1);
execvp ((char *) argv[0], (char **) argv); execvp ((char *) argv[0], (char **) argv);
exit (127); _exit (127);
} }
waitpid (pid, &status, 0); waitpid (pid, &status, 0);
if (!WIFEXITED (status)) if (!WIFEXITED (status))