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SystemServer: Don't let services inherit standard in/out and TTY

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We were letting services inherit writable fds for /dev/tty0, as well as
having /dev/tty0 as their controlling terminal.

Lock this down by closing fds {0,1,2} when spawning a service. We also
detach from the controlling terminal. An exception is made for services
with an explicit StdIO setting. In those cases, we now switch the
controlling terminal to the specified path if possible.
This commit is contained in:
Andreas Kling 2020-01-04 12:17:13 +01:00
parent 755938c650
commit 32d0967f5f
1 changed files with 16 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

20
Servers/SystemServer/Service.cpp
View file

@ -9,6 +9,7 @@
#include <pwd.h>
#include <sched.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <unistd.h>
@ -157,15 +158,26 @@ void Service::spawn()
}
if (!m_stdio_file_path.is_null()) {
close(0);
close(STDIN_FILENO);
int fd = open_with_path_length(m_stdio_file_path.characters(), m_stdio_file_path.length(), O_RDWR, 0);
ASSERT(fd <= 0);
if (fd < 0) {
perror("open");
ASSERT_NOT_REACHED();
}
dup2(0, 1);
dup2(0, 2);
dup2(STDIN_FILENO, STDOUT_FILENO);
dup2(STDIN_FILENO, STDERR_FILENO);
if (isatty(STDIN_FILENO)) {
ioctl(STDIN_FILENO, TIOCSCTTY);
}
} else {
if (isatty(STDIN_FILENO)) {
ioctl(STDIN_FILENO, TIOCNOTTY);
}
close(STDIN_FILENO);
close(STDOUT_FILENO);
close(STDERR_FILENO);
}
if (!m_socket_path.is_null()) {
@ -178,7 +190,7 @@ void Service::spawn()
if (!m_user.is_null()) {
if (setgid(m_gid) < 0 || setuid(m_uid) < 0) {
fprintf(stderr, "Failed to drop privileges (GID=%u, UID=%u)\n", m_gid, m_uid);
dbgprintf("Failed to drop privileges (GID=%u, UID=%u)\n", m_gid, m_uid);
exit(1);
}
}