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util-lib/systemd-run: implement race-free PTY peer opening (#34953)

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This makes use of the new TIOCGPTPEER pty ioctl() for directly opening a
PTY peer, without going via path names. This is nice because it closes a
race around allocating and opening the peer. And also has the nice
benefit that if we acquired an fd originating from some other
namespace/container, we can directly derive the peer fd from it, without
having to reenter the namespace again.
This commit is contained in:
Luca Boccassi
2024-11-01 11:29:19 +00:00
committed by GitHub
parent d86e9b64e4 42c8f1c761
commit fdccba15be
5 changed files with 165 additions and 77 deletions
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src/machine/machine-dbus.c
+8 -5
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@@ -407,7 +407,7 @@ int bus_machine_method_open_shell(sd_bus_message *message, void *userdata, sd_bu
_cleanup_strv_free_ char **env = NULL, **args_wire = NULL, **args = NULL;
_cleanup_free_ char *command_line = NULL;
Machine *m = ASSERT_PTR(userdata);
const char *p, *unit, *user, *path, *description, *utmp_id;
const char *unit, *user, *path, *description, *utmp_id;
int r;
assert(message);
@@ -484,10 +484,11 @@ int bus_machine_method_open_shell(sd_bus_message *message, void *userdata, sd_bu
if (master < 0)
return master;
p = path_startswith(pty_name, "/dev/pts/");
assert(p);
slave = machine_open_terminal(m, pty_name, O_RDWR|O_NOCTTY|O_CLOEXEC);
/* First try to get an fd for the PTY peer via the new racefree ioctl(), directly. Otherwise go via
* joining the namespace, because it goes by path */
slave = pty_open_peer_racefree(master, O_RDWR|O_NOCTTY|O_CLOEXEC);
if (ERRNO_IS_NEG_NOT_SUPPORTED(slave))
slave = machine_open_terminal(m, pty_name, O_RDWR|O_NOCTTY|O_CLOEXEC);
if (slave < 0)
return slave;
@@ -505,6 +506,8 @@ int bus_machine_method_open_shell(sd_bus_message *message, void *userdata, sd_bu
return r;
/* Name and mode */
const char *p = ASSERT_PTR(path_startswith(pty_name, "/dev/pts/"));
unit = strjoina("container-shell@", p, ".service");
r = sd_bus_message_append(tm, "ss", unit, "fail");
if (r < 0)