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dbus-daemon, dbus-launch: cope with callers having closed standard fds

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In Debian bug <https://bugs.debian.org/829348>, lightdm appears to
have been starting dbus-launch with at least one of the three
standard fds 0, 1, 2 (stdin, stdout, stderr) closed. This resulted
in the dbus-daemon's epoll_create1() returning a fd less than 3.
Later, _dbus_become_daemon() replaces fds 0-2 with /dev/null. As a
result, a subsequent call to _dbus_loop_add_watch() for the reload
pipe resulted in calling epoll_ctl on the non-epoll fd pointing to
/dev/null, which fails with EINVAL, resulting in the dbus-daemon
exiting unsuccessfully.

Unix programs are not normally expected to behave correctly when
launched with the standard fds not already open; but at the same time,
X11 autolaunching means that dbus-launch (and hence the dbus-daemon)
can get started from an arbitrarily precarious situation.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=97008
Signed-off-by: Simon McVittie <smcv@debian.org>
Reviewed-by: Thiago Macieira <thiago@kde.org>
This commit is contained in:
Simon McVittie 2016-07-21 08:24:38 +01:00 • committed by Simon McVittie
parent 69123a6bd2
commit c8f73a2a3a
2 changed files with 42 additions and 2 deletions
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25
bus/main.c
View file

@ -42,6 +42,10 @@
#include "apparmor.h"
#include "audit.h"
#ifdef DBUS_UNIX
#include <dbus/dbus-sysdeps-unix.h>
#endif
static BusContext *context;
#ifdef DBUS_UNIX
@ -378,6 +382,27 @@ main (int argc, char **argv)
dbus_bool_t print_address;
dbus_bool_t print_pid;
BusContextFlags flags;
#ifdef DBUS_UNIX
const char *error_str;
/* Redirect stdin from /dev/null since we will never need it, and
* redirect stdout and stderr to /dev/null if not already open.
*
* We should do this as the very first thing, to ensure that when we
* create other file descriptors (for example for epoll, inotify or
* a socket), they never get assigned as fd 0, 1 or 2. If they were,
* which could happen if our caller had (incorrectly) closed those
* standard fds, they'd get closed when we daemonize - for example,
* closing our listening socket would stop us listening, and closing
* a Linux epoll socket would cause the main loop to fail. */
if (!_dbus_ensure_standard_fds (DBUS_FORCE_STDIN_NULL, &error_str))
{
fprintf (stderr,
"dbus-daemon: fatal error setting up standard fds: %s: %s\n",
error_str, _dbus_strerror (errno));
return 1;
}
#endif
if (!_dbus_string_init (&config_file))
return 1;

19
tools/dbus-launch.c
View file

@ -843,10 +843,25 @@ main (int argc, char **argv)
char *config_file;
dbus_bool_t user_bus_supported = FALSE;
DBusString user_bus;
const char *error_str;
exit_with_session = FALSE;
config_file = NULL;
/* Ensure that the first three fds are open, to ensure that when we
* create other file descriptors (for example for epoll, inotify or
* a socket), they never get assigned as fd 0, 1 or 2. If they were,
* which could happen if our caller had (incorrectly) closed those
* standard fds, then we'd start dbus-daemon with those fds closed,
* which is unexpected and could cause it to misbehave. */
if (!_dbus_ensure_standard_fds (0, &error_str))
{
fprintf (stderr,
"dbus-launch: fatal error setting up standard fds: %s: %s\n",
error_str, _dbus_strerror (errno));
return 1;
}
prev_arg = NULL;
i = 1;
while (i < argc)