From: Joseph Sutton <josephsutton@catalyst.net.nz>
Date: Mon, 29 Mar 2021 02:04:53 +0000 (+1300)
Subject: util: Ensure debugger can be attached to process
X-Git-Tag: tevent-0.11.0~1066
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=05a1ca2f4c771d1e249a6d756488cb5e1e3312dd;p=thirdparty%2Fsamba.git

util: Ensure debugger can be attached to process

samba_start_debugger() attempts to start a debugger attached to the
calling process by calling system() to start a background process.
However, if the spawned shell exits before the debugger has had a chance
to attach, the debugger process will no longer be a child of the parent
process (as it will have been reparented).

If the system does not allow tracing by non-child processes, attachment
may fail as a result.

This commit replaces the system() call and the implicit shell around
xterm with an explicit fork()/exec() so that the debugger remains a
child of the calling process, ensuring the attachment succeeds unless
tracing is disabled completely.

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Reviewed-by: Andrew Bartlet <abartlet@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
---

diff --git a/lib/util/util.c b/lib/util/util.c
index 7d7fb91e875..b175b22cf13 100644
--- a/lib/util/util.c
+++ b/lib/util/util.c
@@ -1166,21 +1166,27 @@ void anonymous_shared_free(void *ptr)
 */
 void samba_start_debugger(void)
 {
-	char *cmd = NULL;
+	pid_t pid = fork();
+	if (pid == -1) {
+		return;
+	} else if (pid) {
 #if defined(HAVE_PRCTL) && defined(PR_SET_PTRACER)
-	/*
-	 * Make sure all children can attach a debugger.
-	 */
-	prctl(PR_SET_PTRACER, getpid(), 0, 0, 0);
+		/*
+		 * Make sure the child process can attach a debugger.
+		 */
+		prctl(PR_SET_PTRACER, pid, 0, 0, 0);
 #endif
-	if (asprintf(&cmd, "xterm -e \"gdb --pid %u\"&", getpid()) == -1) {
-		return;
-	}
-	if (system(cmd) == -1) {
+		sleep(2);
+	} else {
+		char *cmd = NULL;
+
+		if (asprintf(&cmd, "gdb --pid %u", getppid()) == -1) {
+			_exit(EXIT_FAILURE);
+		}
+
+		execlp("xterm", "xterm", "-e", cmd, (char *) NULL);
 		free(cmd);
-		return;
+		_exit(errno);
 	}
-	free(cmd);
-	sleep(2);
 }
 #endif