core: redirect LSan's report to /dev/console during manager exit

When exiting PID 1 we most likely don't have stdio/stdout open, so the
final LSan check would not print any actionable information and would
just crash PID 1 leading up to a kernel panic, which is a bit annoying.
Let's instead attempt to open /dev/console, and if we succeed redirect
LSan's report there.

The result is a bit messy, as it's slightly interleaved with the kernel
panic, but it's definitely better than not having the stack trace at
all:

[  OK  ] Reached target final.target.
[  OK  ] Finished systemd-poweroff.service.
[  OK  ] Reached target poweroff.target.

=================================================================
3 1m  43.251782] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100
[   43.252838] CPU: 2 PID: 1 Comm: systemd Not tainted 6.4.12-200.fc38.x86_64 #1
==[1==ERR O R :4 3Le.a2k53562] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
[   43.254683] Call Trace:
[   43.254911]  <TASK>
[   43.255107]  dump_stack_lvl+0x47/0x60
S[ a  43.n2555i05]  panic+t0x192/0x350
izer[   :43.255966 ]  do_exit+0x990/0xdb10
etec[   43.256504]  do_group_exit+0x31/0x80
[   43.256889]  __x64_sys_exit_group+0x18/0x20
[   43.257288]  do_syscall_64+0x60/0x90
o_user_mod leaks[   43.257618]  ? syscall_exit_t

+0x2b/0x40
[   43.258411]  ? do_syscall_64+0x6c/0x90
1mDirect le[   43.258755]  ak of 21 byte(s)? exc_page_fault+0x7f/0x180
[   43.259446]  entry_SYSCALL_64_after_hwframe+0x72/0xdc
 [   43.259901] RiIP: 0033:0x7f357nb8f3ad4
 1 objec[   43.260354] Ctode: 48 89 (f7 0f 05 c3 sf3 0f 1e fa b8 3b 00 00 00) 0f 05 c3 0f 1f 4 0 00 f3 0f 1e fa 50 58 b8 e7 00 00 00 48 83 ec 08 48 63 ff 0f 051
[   43.262581] RSP: 002b:00007ffc25872440 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
a RBX: 00007f357be9b218 RCX: 00007f357b8f3ad4m:ffd
[   43.264512] RDX: 0000000000000001 RSI: 00007f357b933b63 RDI: 0000000000000001
[   43.265355] RBP: 00007f357be9b218 R08: efffffffffffffff R09: 00007ffc258721ef
[   43.266191] R10: 000000000000003f R11: 0000000000000202 R12: 00000fe6ae9e0000
[   43.266891] R13: 00007f3574f00000 R14: 0000000000000000 R15: 0000000000000007
[   43.267517]  </TASK>

    #0 0x7f357b8814a8 in strdup (/lib64/libasan.so.8+0x814a8) (BuildId: e5f0a0d511a659fbc47bf41072869139cb2db47f)
    #1 0x7f3578d43317 in cg_path_decode_unit ../src/basic/cgroup-util.c:1132
    #2 0x7f3578d43936 in cg_path_get_unit ../src/basic/cgroup-util.c:1190
    #3 0x7f3578d440f6 in cg_pid_get_unit ../src/basic/cgroup-util.c:1234
    #4 0x7f35789263d7 in bus_log_caller ../src/shared/bus-util.c:734
    #5 0x7f357a9cf10a in method_reload ../src/core/dbus-manager.c:1621
    #6 0x7f3578f77497 in method_callbacks_run ../src/libsystemd/sd-bus/bus-objects.c:406
    #7 0x7f3578f80dd8 in object_find_and_run ../src/libsystemd/sd-bus/bus-objects.c:1319
    #8 0x7f3578f82487 in bus_process_object ../src/libsystemd/sd-bus/bus-objects.c:1439
    #9 0x7f3578fe41f1 in process_message ../src/libsystemd/sd-bus/sd-bus.c:3007
    #10 0x7f3578fe477b in process_running ../src/libsystemd/sd-bus/sd-bus.c:3049
    #11 0x7f3578fe75d1 in bus_process_internal ../src/libsystemd/sd-bus/sd-bus.c:3269
    #12 0x7f3578fe776e in sd_bus_process ../src/libsystemd/sd-bus/sd-bus.c:3296
    #13 0x7f3578feaedc in io_callback ../src/libsystemd/sd-bus/sd-bus.c:3638
    #14 0x7f35791c2f68 in source_dispatch ../src/libsystemd/sd-event/sd-event.c:4187
    #15 0x7f35791cc6f9 in sd_event_dispatch ../src/libsystemd/sd-event/sd-event.c:4808
    #16 0x7f35791cd830 in sd_event_run ../src/libsystemd/sd-event/sd-event.c:4869
    #17 0x7f357abcd572 in manager_loop ../src/core/manager.c:3244
    #18 0x41db21 in invoke_main_loop ../src/core/main.c:1960
    #19 0x426615 in main ../src/core/main.c:3125
    #20 0x7f3577c49b49 in __libc_start_call_main (/lib64/libc.so.6+0x27b49) (BuildId: 245240a31888ad5c11bbc55b18e02d87388f59a9)
    #21 0x7f3577c49c0a in __libc_start_main_alias_2 (/lib64/libc.so.6+0x27c0a) (BuildId: 245240a31888ad5c11bbc55b18e02d87388f59a9)
    #22 0x408494 in _start (/usr/lib/systemd/systemd+0x408494) (BuildId: fe61e1b0f00b6a36aa34e707a98c15c52f6b960a)

SUMMARY: AddressSanitizer: 21 byte(s) leaked in 1 allocation(s).
[   43.295912] Kernel Offset: 0x7000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[   43.297036] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100 ]---

Originally noticed in #28579.

src/core/main.c

@@ -3181,7 +3181,17 @@ int main(int argc, char *argv[]) {
 #endif
 
 #if HAS_FEATURE_ADDRESS_SANITIZER
+        /* At this stage we most likely don't have stdio/stderr open, so the following
+         * LSan check would not print any actionable information and would just crash
+         * PID 1. To make this a bit more helpful, let's try to open /dev/console,
+         * and if we succeed redirect LSan's report there. */
+
+        int tty_fd = open_terminal("/dev/console", O_WRONLY|O_NOCTTY|O_CLOEXEC);
+        if (tty_fd >= 0)
+            __sanitizer_set_report_fd((void*) (intptr_t) tty_fd);
+
         __lsan_do_leak_check();
+        tty_fd = safe_close(tty_fd);
 #endif
 
         if (r < 0)