From: Todd C. Miller <Todd.Miller@courtesan.com>
Date: Tue, 17 Jan 2012 15:27:33 +0000 (-0500)
Subject: When not logging I/O, use a signal handler that only forwards SIGINT,
X-Git-Tag: SUDO_1_8_4~49^2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2fd77381a1ea06071a439b78e342925f2c5b8fd3;p=sudo

When not logging I/O, use a signal handler that only forwards SIGINT,
SIGQUIT and SIGHUP when they are user-generated signals.  Fixes a
race in the non-I/O logging path where the command may receive two
keyboard-generated signals; one from the kernel and one from the
sudo process.
---

diff --git a/src/exec.c b/src/exec.c
index c70e0cff4..9deb5a25e 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -78,6 +78,9 @@ static int handle_signals(int fd, pid_t child, int log_io,
     struct command_status *cstat);
 static void forward_signals(int fd);
 static void schedule_signal(int signo);
+#ifdef SA_SIGINFO
+static void handler_nofwd(int s, siginfo_t *info, void *context);
+#endif
 
 /*
  * Like execve(2) but falls back to running through /bin/sh
@@ -286,14 +289,28 @@ sudo_execve(struct command_details *details, struct command_status *cstat)
     sa.sa_handler = handler;
     sigaction(SIGALRM, &sa, NULL);
     sigaction(SIGCHLD, &sa, NULL);
-    sigaction(SIGHUP, &sa, NULL);
-    sigaction(SIGINT, &sa, NULL);
     sigaction(SIGPIPE, &sa, NULL);
-    sigaction(SIGQUIT, &sa, NULL);
     sigaction(SIGTERM, &sa, NULL);
     sigaction(SIGUSR1, &sa, NULL);
     sigaction(SIGUSR2, &sa, NULL);
 
+    /*
+     * When not running the command in a pty, we do not want to
+     * forward signals generated by the kernel that the child will
+     * already have received either by virtue of being in the
+     * controlling tty's process group (SIGINT, SIGQUIT) or because
+     * the session is terminating (SIGHUP).
+     */
+#ifdef SA_SIGINFO
+    if (!log_io) {
+	sa.sa_flags |= SA_SIGINFO;
+	sa.sa_sigaction = handler_nofwd;
+    }
+#endif
+    sigaction(SIGHUP, &sa, NULL);
+    sigaction(SIGINT, &sa, NULL);
+    sigaction(SIGQUIT, &sa, NULL);
+
     /* Max fd we will be selecting on. */
     maxfd = MAX(sv[0], signal_pipe[0]);
 
@@ -617,6 +634,30 @@ handler(int s)
 	/* shut up glibc */;
 }
 
+#ifdef SA_SIGINFO
+/*
+ * Generic handler for signals passed from parent -> child.
+ * The other end of signal_pipe is checked in the main event loop.
+ * This version is for the non-pty case and does not forward
+ * signals that are generated by the kernel.
+ */
+static void
+handler_nofwd(int s, siginfo_t *info, void *context)
+{
+    unsigned char signo = (unsigned char)s;
+
+    /* Only forward user-generated signals. */
+    if (info->si_code <= 0) {
+	/*
+	 * The pipe is non-blocking, if we overflow the kernel's pipe
+	 * buffer we drop the signal.  This is not a problem in practice.
+	 */
+	if (write(signal_pipe[1], &signo, sizeof(signo)) == -1)
+	    /* shut up glibc */;
+    }
+}
+#endif /* SA_SIGINFO */
+
 /*
  * Open a pipe and make both ends non-blocking.
  * Returns 0 on success and -1 on error.