Reset the signal handlers at program exit

The signal handler will access the Settings struct, which gets freed at
normal program finalization.

When using leak sanitizers with ASAN_OPTIONS=abort_on_error=1, which
runs after program termination, any leak causes SIGABRT to be raised,
calling the crash handler, which will derefernce the freed Settings.

    ==44741==ERROR: AddressSanitizer: heap-use-after-free on address 0x60d000000080 at pc 0x0000005680df bp 0x7fffe335e960 sp 0x7fffe335e958
    READ of size 8 at 0x60d000000080 thread T0
        #0 0x5680de in Settings_write /home/christian/Coding/workspaces/htop/Settings.c:329:26
        #1 0x4f77b7 in CRT_handleSIGSEGV /home/christian/Coding/workspaces/htop/CRT.c:1020:4
        #2 0x7f8a1120c13f  (/lib/x86_64-linux-gnu/libpthread.so.0+0x1413f)
        #3 0x7f8a11042ce0 in __libc_signal_restore_set signal/../sysdeps/unix/sysv/linux/internal-signals.h:86:3
        #4 0x7f8a11042ce0 in raise signal/../sysdeps/unix/sysv/linux/raise.c:48:3
        #5 0x7f8a1102c536 in abort stdlib/abort.c:79:7
        #6 0x4c3db6 in __sanitizer::Abort() (/home/christian/Coding/workspaces/htop/htop+0x4c3db6)
        #7 0x4c2090 in __sanitizer::Die() (/home/christian/Coding/workspaces/htop/htop+0x4c2090)
        #8 0x4d0a17 in __lsan::HandleLeaks() (/home/christian/Coding/workspaces/htop/htop+0x4d0a17)
        #9 0x4cd950 in __lsan::DoLeakCheck() (/home/christian/Coding/workspaces/htop/htop+0x4cd950)
        #10 0x7f8a110454d6 in __run_exit_handlers stdlib/exit.c:108:8
        #11 0x7f8a11045679 in exit stdlib/exit.c:139:3
        #12 0x7f8a1102dd10 in __libc_start_main csu/../csu/libc-start.c:342:3
        #13 0x428a19 in _start (/home/christian/Coding/workspaces/htop/htop+0x428a19)

    0x60d000000080 is located 64 bytes inside of 144-byte region [0x60d000000040,0x60d0000000d0)
    freed by thread T0 here:
        #0 0x4a4f72 in free (/home/christian/Coding/workspaces/htop/htop+0x4a4f72)
        #1 0x566693 in Settings_delete /home/christian/Coding/workspaces/htop/Settings.c:32:4
        #2 0x4ede10 in CommandLine_run /home/christian/Coding/workspaces/htop/CommandLine.c:393:4
        #3 0x4d6f32 in main /home/christian/Coding/workspaces/htop/htop.c:15:11
        #4 0x7f8a1102dd09 in __libc_start_main csu/../csu/libc-start.c:308:16

    previously allocated by thread T0 here:
        #0 0x4a5372 in __interceptor_calloc (/home/christian/Coding/workspaces/htop/htop+0x4a5372)
        #1 0x57f61a in xCalloc /home/christian/Coding/workspaces/htop/XUtils.c:55:17
        #2 0x5688a6 in Settings_new /home/christian/Coding/workspaces/htop/Settings.c:392:21
        #3 0x4ecb57 in CommandLine_run /home/christian/Coding/workspaces/htop/CommandLine.c:303:25
        #4 0x4d6f32 in main /home/christian/Coding/workspaces/htop/htop.c:15:11
        #5 0x7f8a1102dd09 in __libc_start_main csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: heap-use-after-free /home/christian/Coding/workspaces/htop/Settings.c:329:26 in Settings_write

3 files changed, 37 insertions, 15 deletions

diff --git a/CRT.c b/CRT.c
index 6a87882e..ed78b59e 100644
--- a/CRT.c
+++ b/CRT.c
@@ -817,6 +817,38 @@ static void dumpStderr(void) {
 
 static struct sigaction old_sig_handler[32];
 
+static void CRT_installSignalHandlers(void) {
+   struct sigaction act;
+   sigemptyset (&act.sa_mask);
+   act.sa_flags = (int)SA_RESETHAND | SA_NODEFER;
+   act.sa_handler = CRT_handleSIGSEGV;
+   sigaction (SIGSEGV, &act, &old_sig_handler[SIGSEGV]);
+   sigaction (SIGFPE, &act, &old_sig_handler[SIGFPE]);
+   sigaction (SIGILL, &act, &old_sig_handler[SIGILL]);
+   sigaction (SIGBUS, &act, &old_sig_handler[SIGBUS]);
+   sigaction (SIGPIPE, &act, &old_sig_handler[SIGPIPE]);
+   sigaction (SIGSYS, &act, &old_sig_handler[SIGSYS]);
+   sigaction (SIGABRT, &act, &old_sig_handler[SIGABRT]);
+
+   signal(SIGINT, CRT_handleSIGTERM);
+   signal(SIGTERM, CRT_handleSIGTERM);
+   signal(SIGQUIT, CRT_handleSIGTERM);
+}
+
+void CRT_resetSignalHandlers(void) {
+   sigaction (SIGSEGV, &old_sig_handler[SIGSEGV], NULL);
+   sigaction (SIGFPE, &old_sig_handler[SIGFPE], NULL);
+   sigaction (SIGILL, &old_sig_handler[SIGILL], NULL);
+   sigaction (SIGBUS, &old_sig_handler[SIGBUS], NULL);
+   sigaction (SIGPIPE, &old_sig_handler[SIGPIPE], NULL);
+   sigaction (SIGSYS, &old_sig_handler[SIGSYS], NULL);
+   sigaction (SIGABRT, &old_sig_handler[SIGABRT], NULL);
+
+   signal(SIGINT, SIG_DFL);
+   signal(SIGTERM, SIG_DFL);
+   signal(SIGQUIT, SIG_DFL);
+}
+
 void CRT_init(const Settings* settings, bool allowUnicode) {
    redirectStderr();
 
@@ -875,21 +907,7 @@ void CRT_init(const Settings* settings, bool allowUnicode) {
       }
    }
 
-   struct sigaction act;
-   sigemptyset (&act.sa_mask);
-   act.sa_flags = (int)SA_RESETHAND | SA_NODEFER;
-   act.sa_handler = CRT_handleSIGSEGV;
-   sigaction (SIGSEGV, &act, &old_sig_handler[SIGSEGV]);
-   sigaction (SIGFPE, &act, &old_sig_handler[SIGFPE]);
-   sigaction (SIGILL, &act, &old_sig_handler[SIGILL]);
-   sigaction (SIGBUS, &act, &old_sig_handler[SIGBUS]);
-   sigaction (SIGPIPE, &act, &old_sig_handler[SIGPIPE]);
-   sigaction (SIGSYS, &act, &old_sig_handler[SIGSYS]);
-   sigaction (SIGABRT, &act, &old_sig_handler[SIGABRT]);
-
-   signal(SIGINT, CRT_handleSIGTERM);
-   signal(SIGTERM, CRT_handleSIGTERM);
-   signal(SIGQUIT, CRT_handleSIGTERM);
+   CRT_installSignalHandlers();
 
    use_default_colors();
    if (!has_colors())
diff --git a/CRT.h b/CRT.h
index 9f3ecb44..4e6ff672 100644
--- a/CRT.h
+++ b/CRT.h
@@ -176,6 +176,8 @@ void CRT_init(const Settings* settings, bool allowUnicode);
 
 void CRT_done(void);
 
+void CRT_resetSignalHandlers(void);
+
 int CRT_readKey(void);
 
 void CRT_disableDelay(void);
diff --git a/CommandLine.c b/CommandLine.c
index b4144d8d..ecfc731e 100644
--- a/CommandLine.c
+++ b/CommandLine.c
@@ -389,6 +389,8 @@ int CommandLine_run(const char* name, int argc, char** argv) {
    if (flags.pidMatchList)
       Hashtable_delete(flags.pidMatchList);
 
+   CRT_resetSignalHandlers();
+
    /* Delete these last, since they can get accessed in the crash handler */
    Settings_delete(settings);
    if (dc)