Merge pull request #873 from brauner/bugfix_branch

lxc-attach: fix redirection - stderr

src/lxc/lxc_attach.c

@@ -273,7 +273,39 @@ static int get_pty_on_host(struct lxc_container *c, struct wrapargs *wrap, int *
 	if (lxc_console_create(conf) < 0)
 		return -1;
 	ts = conf->console.tty_state;
-	ts->stdoutfd = STDOUT_FILENO;
+	/*
+	 * We need to make sure that the ouput that is produced inside the
+	 * container is received on the host. Suppose we want to run
+	 *
+	 *	lxc-attach -n a -- /bin/sh -c 'hostname >&2' > /dev/null
+	 *
+	 * This command produces output on stderr inside the container. On the
+	 * host we close stdout by redirecting it to /dev/null. But stderr is,
+	 * as expected, still connected to a tty. We receive the output produced
+	 * on stderr in the container on stderr on the host.
+	 *
+	 * For the command
+	 *
+	 *	lxc-attach -n a -- /bin/sh -c 'hostname >&2' 2> /dev/null
+	 *
+	 * the logic is analogous but because we now have closed stderr on the
+	 * host no output will be received.
+	 *
+	 * Finally, imagine a more complicated case
+	 *
+	 *	lxc-attach -n a -- /bin/sh -c 'echo OUT; echo ERR >&2' > /tmp/out 2> /tmp/err
+	 *
+	 * Here, we produce output in the container on stdout and stderr. On the
+	 * host we redirect stdout and stderr to files. Because of that stdout
+	 * and stderr are not dup2()ed. Thus, they are not connected to a pty
+	 * and output on stdout and stderr is redirected to the corresponding
+	 * files as expected.
+	 */
+	if (!isatty(STDOUT_FILENO) && isatty(STDERR_FILENO))
+		ts->stdoutfd = STDERR_FILENO;
+	else
+		ts->stdoutfd = STDOUT_FILENO;
+
 	conf->console.descr = &descr;
 
 	/* Shift ttys to container. */

src/tests/Makefile.am

@@ -52,6 +52,7 @@ bin_SCRIPTS = lxc-test-autostart lxc-test-cloneconfig lxc-test-createconfig
 
 if DISTRO_UBUNTU
 bin_SCRIPTS += \
+	lxc-test-lxc-attach \
 	lxc-test-apparmor-mount \
 	lxc-test-checkpoint-restore \
 	lxc-test-snapdeps \
@@ -77,6 +78,7 @@ EXTRA_DIST = \
 	list.c \
 	locktests.c \
 	lxcpath.c \
+	lxc-test-lxc-attach \
 	lxc-test-autostart \
 	lxc-test-apparmor-mount \
 	lxc-test-checkpoint-restore \

src/tests/lxc-test-lxc-attach

@@ -0,0 +1,135 @@
+#!/bin/sh
+
+# lxc: linux Container library
+
+# Authors:
+# Christian Brauner <christian.brauner@mailbox.org>
+#
+# This is a test script for the lxc-attach program. It tests whether I/O
+# redirection works correctly.
+
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+set -e
+
+FAIL() {
+	echo -n "Failed " >&2
+	echo "$*" >&2
+        lxc-destroy -n busy -f
+	exit 1
+}
+
+# Create a container, start it and wait for it to be in running state
+lxc-create -t busybox -n busy || FAIL "creating busybox container"
+lxc-start -n busy -d || FAIL "starting busybox container"
+lxc-wait -n busy -s RUNNING || FAIL "waiting for busybox container to run"
+
+# Test if simple attach is working
+# - stdin  --> attached to pty
+# - stdout --> attached to pty
+# - stderr --> attached to pty
+attach=$(lxc-attach -n busy -- hostname) # expect output
+if [ "$attach" != "busy" ]; then
+        FAIL " simple attach"
+fi
+
+# Test if we still receive output when stdin does not refer to a tty
+# - stdin  --> /dev/null
+# - stdout --> attached to pty
+# - stderr --> attached to pty
+attach=$(lxc-attach -n busy -- hostname < /dev/null) # expect output
+if [ "$attach" != "busy" ]; then
+        FAIL " with stdin redirection < /dev/null"
+fi
+
+# Test if we are silent when stdout does not refer to a tty
+# - stdin  --> attached to pty
+# - stdout --> /dev/null
+# - stderr --> attached to pty
+attach=$(lxc-attach -n busy -- hostname > /dev/null) # expect no output
+if [ -n "$attach" ]; then
+        FAIL " with stdout redirection > /dev/null"
+fi
+
+# Test if we are silent when stdout and stdin do not refer to a tty
+# - stdin  --> /dev/null
+# - stdout --> /dev/null
+# - stderr --> attached to pty
+attach=$(lxc-attach -n busy -- hostname > /dev/null < /dev/null) # expect no output
+if [ -n "$attach" ]; then
+        FAIL " with stdin and stdout redirection > /dev/null < /dev/null"
+fi
+
+# Test if we still receive output when stdin and stderr do not refer to a tty
+# - stdin  --> /dev/null
+# - stdout --> attached to pty
+# - stderr --> /dev/null
+attach=$(lxc-attach -n busy -- hostname 2> /dev/null < /dev/null) # expect output
+if [ "$attach" != "busy" ]; then
+        FAIL " with stdin and stderr redirection 2> /dev/null < /dev/null"
+fi
+
+# - produce output on stderr in container
+# - redirect stdout on host to /dev/null
+# - output on host should be received on stderr
+# - to capture the ouput on stderr on the host we redirect stderr on the host to
+#   stdout
+# - stdin  --> attached to pty
+# - stdout --> /dev/null
+# - stderr --> attached to pty
+attach=$( ( lxc-attach -n busy -- sh -c 'hostname >&2' > /dev/null ) 2>&1 )
+if [ "$attach" != "busy" ]; then
+        FAIL " bla sh -c 'hostname >&2' >/dev/null"
+fi
+
+# - produce output on stderr in container
+# - redirect stderr on host to /dev/null
+# - no output from container should be received on stderr on host
+# - stdin  --> attached to pty
+# - stdout --> attached to pty
+# - stderr --> /dev/null
+attach=$( ( lxc-attach -n busy -- sh -c 'hostname >&2' 2> /dev/null ) 2>&1 )
+if [ -n "$attach" ]; then
+        FAIL " bla sh -c 'hostname >&2' 2> /dev/null"
+fi
+
+# Test file redirection
+# - stdin  --> attached to pty
+# - stdout --> /dev/null
+# - stderr --> /dev/null
+out=$(mktemp /tmp/out_XXXX)
+err=$(mktemp /tmp/err_XXXX)
+lxc-attach -n busy -- sh -c 'echo OUT; echo ERR >&2' > $out 2> $err
+outcontent=$(cat $out)
+errcontent=$(cat $err)
+if [ "$outcontent" != "OUT" ] || [ "$errcontent" != "ERR" ]; then
+        FAIL " bla sh -c 'echo OUT; echo ERR >&2' > $out 2> $err"
+fi
+
+# Test stdin input
+# - stdin  --> $in
+# - stdout --> attached to pty
+# - stderr --> attached to pty
+in=$(mktemp /tmp/in_XXXX)
+echo '#!/bin/sh' > $in
+echo hostname >> $in
+attach=$(lxc-attach -n busy -- < $in)
+if [ "$attach" != "busy" ]; then
+        FAIL " < $in"
+fi
+
+lxc-destroy -n busy -f
+
+exit 0