main/lxc: security fix for CVE-2015-1335

2 files changed, 641 insertions, 1 deletions

diff --git a/main/lxc/APKBUILD b/main/lxc/APKBUILD
index bbd8a83249..8da83e9c06 100644
--- a/main/lxc/APKBUILD
+++ b/main/lxc/APKBUILD
@@ -4,7 +4,7 @@
 pkgname=lxc
 pkgver=1.1.3
 _mypkgver=${pkgver/_rc/.rc}
-pkgrel=1
+pkgrel=2
 pkgdesc="linux containers - tools"
 url="http://lxc.sourceforge.net/"
 arch="all"
@@ -20,6 +20,7 @@ subpackages="$pkgname-dev $pkgname-doc $pkgname-lvm lua5.2-lxc:_lua52
 source="https://github.com/lxc/lxc/archive/lxc-$_mypkgver.tar.gz
 	0001-Clone-bridge-interface-MTU-setting.patch
 	version.patch
+	CVE-2015-1335.patch
 	lxc.initd
 	"
 
@@ -91,12 +92,15 @@ dev() {
 md5sums="680198729359bd5e58dc14ce617e72b1  lxc-1.1.3.tar.gz
 d41088af5dee2e2df7975bb33d5d1537  0001-Clone-bridge-interface-MTU-setting.patch
 79e90616b5049a472ccdcb5b1dcdd8b1  version.patch
+7327d4e94f1f23473d82c1fe98706eb2  CVE-2015-1335.patch
 1e47412382517ee2adcbca00f07377ca  lxc.initd"
 sha256sums="b75fb8e376d3313e152f31fb7372b68f33a953a12191a39de4cded04fff94300  lxc-1.1.3.tar.gz
 e9a6c2e5f98a5f03bf772333c91efe7dafbc4f8d699dced73859e7d6c98d2d42  0001-Clone-bridge-interface-MTU-setting.patch
 b6d85fb23940d2511b3951de56b2532843c0e03ec1613548366361cc0c1a46b9  version.patch
+85af34f968ed1e00de357c2ff6d3234c144f53878a707d1d5f8d864407f23726  CVE-2015-1335.patch
 ce4c30c65832c4b79df1c3c1ef6a444247e2866ab24690f1476e7b98b722fac1  lxc.initd"
 sha512sums="cafa4fbe4fe23b8c0b98007a79f20899c4a3b98c51d797b9c16e38dfec1eee5a513b58621308fe6551707d38028d9e5bd78ade8822691ffe4a7a369b10a48dda  lxc-1.1.3.tar.gz
 6c4dc0a53ba8947a37faa14bb81a7bbed7a88fb118513842f5a5a37e9d23fbd2bee4f8f513d3f686a34d373869008ee5ccbd4b9e20615d4b9e4b8139119adce3  0001-Clone-bridge-interface-MTU-setting.patch
 e2ffcbf55447291a8434a4f37255c3a6a119bc4116c75d205006aa2b070bf6be28535cf6107bead14bbf64bf9fa415346ab544bd1c15e1add7d1c6380e6b2def  version.patch
+d8b0a7827a96a4d5c10e7ebf7ca65f415f6895d3b6371cfc1edda2a9a07ea99b9d3db5d8e5cc542ad88b25e717534755faa9938901183a90c7587d83d3fa81aa  CVE-2015-1335.patch
 4ff815d354f022854535a0069033f314263623ead48220d732683d5a268f14f221cbfe1aa9515adf1c2e47de71f1b1f1dda374a1f5f15d6f7025d2de91143d9a  lxc.initd"
diff --git a/main/lxc/CVE-2015-1335.patch b/main/lxc/CVE-2015-1335.patch
new file mode 100644
index 0000000000..719816e48a
--- /dev/null
+++ b/main/lxc/CVE-2015-1335.patch
@@ -0,0 +1,636 @@
+From 1f9cc4943b640d9355709432a705e5fa6e9ad4df Mon Sep 17 00:00:00 2001
+From: Serge Hallyn <serge.hallyn@ubuntu.com>
+Date: Mon, 31 Aug 2015 12:57:20 -0500
+Subject: [PATCH 1/1] Protect container mounts against symlinks
+
+When a container starts up, lxc sets up the container's inital fstree
+by doing a bunch of mounting, guided by the container configuration
+file.  The container config is owned by the admin or user on the host,
+so we do not try to guard against bad entries.  However, since the
+mount target is in the container, it's possible that the container admin
+could divert the mount with symbolic links.  This could bypass proper
+container startup (i.e. confinement of a root-owned container by the
+restrictive apparmor policy, by diverting the required write to
+/proc/self/attr/current), or bypass the (path-based) apparmor policy
+by diverting, say, /proc to /mnt in the container.
+
+To prevent this,
+
+1. do not allow mounts to paths containing symbolic links
+
+2. do not allow bind mounts from relative paths containing symbolic
+links.
+
+Details:
+
+Define safe_mount which ensures that the container has not inserted any
+symbolic links into any mount targets for mounts to be done during
+container setup.
+
+The host's mount path may contain symbolic links.  As it is under the
+control of the administrator, that's ok.  So safe_mount begins the check
+for symbolic links after the rootfs->mount, by opening that directory.
+
+It opens each directory along the path using openat() relative to the
+parent directory using O_NOFOLLOW.  When the target is reached, it
+mounts onto /proc/self/fd/<targetfd>.
+
+Use safe_mount() in mount_entry(), when mounting container proc,
+and when needed.  In particular, safe_mount() need not be used in
+any case where:
+
+1. the mount is done in the container's namespace
+2. the mount is for the container's rootfs
+3. the mount is relative to a tmpfs or proc/sysfs which we have
+   just safe_mount()ed ourselves
+
+Since we were using proc/net as a temporary placeholder for /proc/sys/net
+during container startup, and proc/net is a symbolic link, use proc/tty
+instead.
+
+Update the lxc.container.conf manpage with details about the new
+restrictions.
+
+Finally, add a testcase to test some symbolic link possibilities.
+
+Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
+---
+ doc/lxc.container.conf.sgml.in |  12 +++
+ src/lxc/cgfs.c                 |   5 +-
+ src/lxc/cgmanager.c            |   4 +-
+ src/lxc/conf.c                 |  29 ++---
+ src/lxc/utils.c                | 235 ++++++++++++++++++++++++++++++++++++++++-
+ src/lxc/utils.h                |   2 +
+ src/tests/Makefile.am          |   2 +
+ src/tests/lxc-test-symlink     |  88 +++++++++++++++
+ 8 files changed, 359 insertions(+), 18 deletions(-)
+ create mode 100644 src/tests/lxc-test-symlink
+
+diff --git a/doc/lxc.container.conf.sgml.in b/doc/lxc.container.conf.sgml.in
+index 50c6a2a..0a1ec5f 100644
+--- a/doc/lxc.container.conf.sgml.in
++++ b/doc/lxc.container.conf.sgml.in
+@@ -699,6 +699,18 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+         container. This is useful to mount /etc, /var or /home for
+         examples.
+       </para>
++      <para>
++	NOTE - LXC will generally ensure that mount targets and relative
++	bind-mount sources are properly confined under the container
++	root, to avoid attacks involving over-mounting host directories
++	and files.  (Symbolic links in absolute mount sources are ignored)
++	However, if the container configuration first mounts a directory which
++	is under the control of the container user, such as /home/joe, into
++        the container at some <filename>path</filename>, and then mounts
++        under <filename>path</filename>, then a TOCTTOU attack would be
++        possible where the container user modifies a symbolic link under
++        his home directory at just the right time.
++      </para>
+       <variablelist>
+         <varlistentry>
+           <term>
+diff --git a/src/lxc/cgfs.c b/src/lxc/cgfs.c
+index fcb3cde..df2e6b2 100644
+--- a/src/lxc/cgfs.c
++++ b/src/lxc/cgfs.c
+@@ -1363,7 +1363,10 @@ static bool cgroupfs_mount_cgroup(void *hdata, const char *root, int type)
+ 	if (!path)
+ 		return false;
+ 	snprintf(path, bufsz, "%s/sys/fs/cgroup", root);
+-	r = mount("cgroup_root", path, "tmpfs", MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_RELATIME, "size=10240k,mode=755");
++	r = safe_mount("cgroup_root", path, "tmpfs",
++			MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_RELATIME,
++			"size=10240k,mode=755",
++			root);
+ 	if (r < 0) {
+ 		SYSERROR("could not mount tmpfs to /sys/fs/cgroup in the container");
+ 		return false;
+diff --git a/src/lxc/cgmanager.c b/src/lxc/cgmanager.c
+index c143bea..779a1d8 100644
+--- a/src/lxc/cgmanager.c
++++ b/src/lxc/cgmanager.c
+@@ -1477,7 +1477,7 @@ static bool cgm_bind_dir(const char *root, const char *dirname)
+ 	}
+ 
+ 	/* mount a tmpfs there so we can create subdirs */
+-	if (mount("cgroup", cgpath, "tmpfs", 0, "size=10000,mode=755")) {
++	if (safe_mount("cgroup", cgpath, "tmpfs", 0, "size=10000,mode=755", root)) {
+ 		SYSERROR("Failed to mount tmpfs at %s", cgpath);
+ 		return false;
+ 	}
+@@ -1488,7 +1488,7 @@ static bool cgm_bind_dir(const char *root, const char *dirname)
+ 		return false;
+ 	}
+ 
+-	if (mount(dirname, cgpath, "none", MS_BIND, 0)) {
++	if (safe_mount(dirname, cgpath, "none", MS_BIND, 0, root)) {
+ 		SYSERROR("Failed to bind mount %s to %s", dirname, cgpath);
+ 		return false;
+ 	}
+diff --git a/src/lxc/conf.c b/src/lxc/conf.c
+index d37112b..8cff919 100644
+--- a/src/lxc/conf.c
++++ b/src/lxc/conf.c
+@@ -763,10 +763,11 @@ static int lxc_mount_auto_mounts(struct lxc_conf *conf, int flags, struct lxc_ha
+ 		 * 2.6.32...
+ 		 */
+ 		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "proc",                                              "%r/proc",                      "proc",     MS_NODEV|MS_NOEXEC|MS_NOSUID,   NULL },
+-		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "%r/proc/sys/net",                                   "%r/proc/net",                  NULL,       MS_BIND,                        NULL },
++		/* proc/tty is used as a temporary placeholder for proc/sys/net which we'll move back in a few steps */
++		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "%r/proc/sys/net",                                   "%r/proc/tty",                  NULL,       MS_BIND,                        NULL },
+ 		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "%r/proc/sys",                                       "%r/proc/sys",                  NULL,       MS_BIND,                        NULL },
+ 		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, NULL,                                                "%r/proc/sys",                  NULL,       MS_REMOUNT|MS_BIND|MS_RDONLY,   NULL },
+-		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "%r/proc/net",                                       "%r/proc/sys/net",              NULL,       MS_MOVE,                        NULL },
++		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "%r/proc/tty",                                       "%r/proc/sys/net",              NULL,       MS_MOVE,                        NULL },
+ 		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, "%r/proc/sysrq-trigger",                             "%r/proc/sysrq-trigger",        NULL,       MS_BIND,                        NULL },
+ 		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_MIXED, NULL,                                                "%r/proc/sysrq-trigger",        NULL,       MS_REMOUNT|MS_BIND|MS_RDONLY,   NULL },
+ 		{ LXC_AUTO_PROC_MASK, LXC_AUTO_PROC_RW,    "proc",                                              "%r/proc",                      "proc",     MS_NODEV|MS_NOEXEC|MS_NOSUID,   NULL },
+@@ -809,7 +810,7 @@ static int lxc_mount_auto_mounts(struct lxc_conf *conf, int flags, struct lxc_ha
+ 			}
+ 			mflags = add_required_remount_flags(source, destination,
+ 					default_mounts[i].flags);
+-			r = mount(source, destination, default_mounts[i].fstype, mflags, default_mounts[i].options);
++			r = safe_mount(source, destination, default_mounts[i].fstype, mflags, default_mounts[i].options, conf->rootfs.path ? conf->rootfs.mount : NULL);
+ 			saved_errno = errno;
+ 			if (r < 0 && errno == ENOENT) {
+ 				INFO("Mount source or target for %s on %s doesn't exist. Skipping.", source, destination);
+@@ -1161,7 +1162,7 @@ static int mount_autodev(const char *name, char *root, const char *lxcpath)
+ 		return 0;
+ 	}
+ 
+-	if (mount("none", path, "tmpfs", 0, "size=100000,mode=755")) {
++	if (safe_mount("none", path, "tmpfs", 0, "size=100000,mode=755", root)) {
+ 		SYSERROR("Failed mounting tmpfs onto %s\n", path);
+ 		return false;
+ 	}
+@@ -1246,7 +1247,7 @@ static int fill_autodev(const char *root)
+ 				return -1;
+ 			}
+ 			fclose(pathfile);
+-			if (mount(hostpath, path, 0, MS_BIND, NULL) != 0) {
++			if (safe_mount(hostpath, path, 0, MS_BIND, NULL, root) != 0) {
+ 				SYSERROR("Failed bind mounting device %s from host into container",
+ 					d->name);
+ 				return -1;
+@@ -1499,7 +1500,7 @@ static int setup_dev_console(const struct lxc_rootfs *rootfs,
+ 		return -1;
+ 	}
+ 
+-	if (mount(console->name, path, "none", MS_BIND, 0)) {
++	if (safe_mount(console->name, path, "none", MS_BIND, 0, rootfs->mount)) {
+ 		ERROR("failed to mount '%s' on '%s'", console->name, path);
+ 		return -1;
+ 	}
+@@ -1554,7 +1555,7 @@ static int setup_ttydir_console(const struct lxc_rootfs *rootfs,
+ 		return 0;
+ 	}
+ 
+-	if (mount(console->name, lxcpath, "none", MS_BIND, 0)) {
++	if (safe_mount(console->name, lxcpath, "none", MS_BIND, 0, rootfs->mount)) {
+ 		ERROR("failed to mount '%s' on '%s'", console->name, lxcpath);
+ 		return -1;
+ 	}
+@@ -1704,13 +1705,13 @@ static char *get_field(char *src, int nfields)
+ 
+ static int mount_entry(const char *fsname, const char *target,
+ 		       const char *fstype, unsigned long mountflags,
+-		       const char *data, int optional)
++		       const char *data, int optional, const char *rootfs)
+ {
+ #ifdef HAVE_STATVFS
+ 	struct statvfs sb;
+ #endif
+ 
+-	if (mount(fsname, target, fstype, mountflags & ~MS_REMOUNT, data)) {
++	if (safe_mount(fsname, target, fstype, mountflags & ~MS_REMOUNT, data, rootfs)) {
+ 		if (optional) {
+ 			INFO("failed to mount '%s' on '%s' (optional): %s", fsname,
+ 			     target, strerror(errno));
+@@ -1757,7 +1758,7 @@ static int mount_entry(const char *fsname, const char *target,
+ #endif
+ 
+ 		if (mount(fsname, target, fstype,
+-			  mountflags | MS_REMOUNT, data)) {
++			  mountflags | MS_REMOUNT, data) < 0) {
+ 			if (optional) {
+ 				INFO("failed to mount '%s' on '%s' (optional): %s",
+ 					 fsname, target, strerror(errno));
+@@ -1843,7 +1844,7 @@ static inline int mount_entry_on_systemfs(struct mntent *mntent)
+ 	}
+ 
+ 	ret = mount_entry(mntent->mnt_fsname, mntent->mnt_dir,
+-			  mntent->mnt_type, mntflags, mntdata, optional);
++			  mntent->mnt_type, mntflags, mntdata, optional, NULL);
+ 
+ 	free(pathdirname);
+ 	free(mntdata);
+@@ -1930,7 +1931,7 @@ skipabs:
+ 	}
+ 
+ 	ret = mount_entry(mntent->mnt_fsname, path, mntent->mnt_type,
+-			  mntflags, mntdata, optional);
++			  mntflags, mntdata, optional, rootfs->mount);
+ 
+ 	free(mntdata);
+ 
+@@ -1986,7 +1987,7 @@ static int mount_entry_on_relative_rootfs(struct mntent *mntent,
+ 	}
+ 
+ 	ret = mount_entry(mntent->mnt_fsname, path, mntent->mnt_type,
+-			  mntflags, mntdata, optional);
++			  mntflags, mntdata, optional, rootfs);
+ 
+ 	free(pathdirname);
+ 	free(mntdata);
+@@ -3646,7 +3647,7 @@ void lxc_execute_bind_init(struct lxc_conf *conf)
+ 		fclose(pathfile);
+ 	}
+ 
+-	ret = mount(path, destpath, "none", MS_BIND, NULL);
++	ret = safe_mount(path, destpath, "none", MS_BIND, NULL, conf->rootfs.mount);
+ 	if (ret < 0)
+ 		SYSERROR("Failed to bind lxc.init.static into container");
+ 	INFO("lxc.init.static bound into container at %s", path);
+diff --git a/src/lxc/utils.c b/src/lxc/utils.c
+index 7ced314..70d12d5 100644
+--- a/src/lxc/utils.c
++++ b/src/lxc/utils.c
+@@ -1403,6 +1403,239 @@ int setproctitle(char *title)
+ }
+ 
+ /*
++ * @path:    a pathname where / replaced with '\0'.
++ * @offsetp: pointer to int showing which path segment was last seen.
++ *           Updated on return to reflect the next segment.
++ * @fulllen: full original path length.
++ * Returns a pointer to the next path segment, or NULL if done.
++ */
++static char *get_nextpath(char *path, int *offsetp, int fulllen)
++{
++	int offset = *offsetp;
++
++	if (offset >= fulllen)
++		return NULL;
++
++	while (path[offset] != '\0' && offset < fulllen)
++		offset++;
++	while (path[offset] == '\0' && offset < fulllen)
++		offset++;
++
++	*offsetp = offset;
++	return (offset < fulllen) ? &path[offset] : NULL;
++}
++
++/*
++ * Check that @subdir is a subdir of @dir.  @len is the length of
++ * @dir (to avoid having to recalculate it).
++ */
++static bool is_subdir(const char *subdir, const char *dir, size_t len)
++{
++	size_t subdirlen = strlen(subdir);
++
++	if (subdirlen < len)
++		return false;
++	if (strncmp(subdir, dir, len) != 0)
++		return false;
++	if (dir[len-1] == '/')
++		return true;
++	if (subdir[len] == '/' || subdirlen == len)
++		return true;
++	return false;
++}
++
++/*
++ * Check if the open fd is a symlink.  Return -ELOOP if it is.  Return
++ * -ENOENT if we couldn't fstat.  Return 0 if the fd is ok.
++ */
++static int check_symlink(int fd)
++{
++	struct stat sb;
++	int ret = fstat(fd, &sb);
++	if (ret < 0)
++		return -ENOENT;
++	if (S_ISLNK(sb.st_mode))
++		return -ELOOP;
++	return 0;
++}
++
++/*
++ * Open a file or directory, provided that it contains no symlinks.
++ *
++ * CAVEAT: This function must not be used for other purposes than container
++ * setup before executing the container's init
++ */
++static int open_if_safe(int dirfd, const char *nextpath)
++{
++	int newfd = openat(dirfd, nextpath, O_RDONLY | O_NOFOLLOW);
++	if (newfd >= 0) // was not a symlink, all good
++		return newfd;
++
++	if (errno == ELOOP)
++		return newfd;
++
++	if (errno == EPERM || errno == EACCES) {
++		/* we're not root (cause we got EPERM) so
++		   try opening with O_PATH */
++		newfd = openat(dirfd, nextpath, O_PATH | O_NOFOLLOW);
++		if (newfd >= 0) {
++			/* O_PATH will return an fd for symlinks.  We know
++			 * nextpath wasn't a symlink at last openat, so if fd
++			 * is now a link, then something * fishy is going on
++			 */
++			int ret = check_symlink(newfd);
++			if (ret < 0) {
++				close(newfd);
++				newfd = ret;
++			}
++		}
++	}
++
++	return newfd;
++}
++
++/*
++ * Open a path intending for mounting, ensuring that the final path
++ * is inside the container's rootfs.
++ *
++ * CAVEAT: This function must not be used for other purposes than container
++ * setup before executing the container's init
++ *
++ * @target: path to be opened
++ * @prefix_skip: a part of @target in which to ignore symbolic links.  This
++ * would be the container's rootfs.
++ *
++ * Return an open fd for the path, or <0 on error.
++ */
++static int open_without_symlink(const char *target, const char *prefix_skip)
++{
++	int curlen = 0, dirfd, fulllen, i;
++	char *dup = NULL;
++
++	fulllen = strlen(target);
++
++	/* make sure prefix-skip makes sense */
++	if (prefix_skip) {
++		curlen = strlen(prefix_skip);
++		if (!is_subdir(target, prefix_skip, curlen)) {
++			ERROR("WHOA there - target '%s' didn't start with prefix '%s'",
++				target, prefix_skip);
++			return -EINVAL;
++		}
++		/*
++		 * get_nextpath() expects the curlen argument to be
++		 * on a  (turned into \0) / or before it, so decrement
++		 * curlen to make sure that happens
++		 */
++		if (curlen)
++			curlen--;
++	} else {
++		prefix_skip = "/";
++		curlen = 0;
++	}
++
++	/* Make a copy of target which we can hack up, and tokenize it */
++	if ((dup = strdup(target)) == NULL) {
++		SYSERROR("Out of memory checking for symbolic link");
++		return -ENOMEM;
++	}
++	for (i = 0; i < fulllen; i++) {
++		if (dup[i] == '/')
++			dup[i] = '\0';
++	}
++
++	dirfd = open(prefix_skip, O_RDONLY);
++	if (dirfd < 0)
++		goto out;
++	while (1) {
++		int newfd, saved_errno;
++		char *nextpath;
++
++		if ((nextpath = get_nextpath(dup, &curlen, fulllen)) == NULL)
++			goto out;
++		newfd = open_if_safe(dirfd, nextpath);
++		saved_errno = errno;
++		close(dirfd);
++		dirfd = newfd;
++		if (newfd < 0) {
++			errno = saved_errno;
++			if (errno == ELOOP)
++				SYSERROR("%s in %s was a symbolic link!", nextpath, target);
++			else
++				SYSERROR("Error examining %s in %s", nextpath, target);
++			goto out;
++		}
++	}
++
++out:
++	free(dup);
++	return dirfd;
++}
++
++/*
++ * Safely mount a path into a container, ensuring that the mount target
++ * is under the container's @rootfs.  (If @rootfs is NULL, then the container
++ * uses the host's /)
++ *
++ * CAVEAT: This function must not be used for other purposes than container
++ * setup before executing the container's init
++ */
++int safe_mount(const char *src, const char *dest, const char *fstype,
++		unsigned long flags, const void *data, const char *rootfs)
++{
++	int srcfd = -1, destfd, ret, saved_errno;
++	char srcbuf[50], destbuf[50]; // only needs enough for /proc/self/fd/<fd>
++	const char *mntsrc = src;
++
++	if (!rootfs)
++		rootfs = "";
++
++	/* todo - allow symlinks for relative paths if 'allowsymlinks' option is passed */
++	if (flags & MS_BIND && src && src[0] != '/') {
++		INFO("this is a relative bind mount");
++		srcfd = open_without_symlink(src, NULL);
++		if (srcfd < 0)
++			return srcfd;
++		ret = snprintf(srcbuf, 50, "/proc/self/fd/%d", srcfd);
++		if (ret < 0 || ret > 50) {
++			close(srcfd);
++			ERROR("Out of memory");
++			return -EINVAL;
++		}
++		mntsrc = srcbuf;
++	}
++
++	destfd = open_without_symlink(dest, rootfs);
++	if (destfd < 0) {
++		if (srcfd != -1)
++			close(srcfd);
++		return destfd;
++	}
++
++	ret = snprintf(destbuf, 50, "/proc/self/fd/%d", destfd);
++	if (ret < 0 || ret > 50) {
++		if (srcfd != -1)
++			close(srcfd);
++		close(destfd);
++		ERROR("Out of memory");
++		return -EINVAL;
++	}
++
++	ret = mount(mntsrc, destbuf, fstype, flags, data);
++	saved_errno = errno;
++	if (srcfd != -1)
++		close(srcfd);
++	close(destfd);
++	if (ret < 0) {
++		errno = saved_errno;
++		SYSERROR("Failed to mount %s onto %s", src, dest);
++		return ret;
++	}
++
++	return 0;
++}
++
++/*
+  * Mount a proc under @rootfs if proc self points to a pid other than
+  * my own.  This is needed to have a known-good proc mount for setting
+  * up LSMs both at container startup and attach.
+@@ -1440,7 +1673,7 @@ int mount_proc_if_needed(const char *rootfs)
+ 	return 0;
+ 
+ domount:
+-	if (mount("proc", path, "proc", 0, NULL))
++	if (safe_mount("proc", path, "proc", 0, NULL, rootfs) < 0)
+ 		return -1;
+ 	INFO("Mounted /proc in container for security transition");
+ 	return 1;
+diff --git a/src/lxc/utils.h b/src/lxc/utils.h
+index ee12dde..059026f 100644
+--- a/src/lxc/utils.h
++++ b/src/lxc/utils.h
+@@ -279,6 +279,8 @@ bool switch_to_ns(pid_t pid, const char *ns);
+ int is_dir(const char *path);
+ char *get_template_path(const char *t);
+ int setproctitle(char *title);
++int safe_mount(const char *src, const char *dest, const char *fstype,
++		unsigned long flags, const void *data, const char *rootfs);
+ int mount_proc_if_needed(const char *rootfs);
+ int null_stdfds(void);
+ #endif /* __LXC_UTILS_H */
+diff --git a/src/tests/Makefile.am b/src/tests/Makefile.am
+index 461d869..8af9baa 100644
+--- a/src/tests/Makefile.am
++++ b/src/tests/Makefile.am
+@@ -54,6 +54,7 @@ if DISTRO_UBUNTU
+ bin_SCRIPTS += \
+ 	lxc-test-apparmor-mount \
+ 	lxc-test-checkpoint-restore \
++	lxc-test-symlink \
+ 	lxc-test-ubuntu \
+ 	lxc-test-unpriv \
+ 	lxc-test-usernic
+@@ -80,6 +81,7 @@ EXTRA_DIST = \
+ 	lxc-test-checkpoint-restore \
+ 	lxc-test-cloneconfig \
+ 	lxc-test-createconfig \
++	lxc-test-symlink \
+ 	lxc-test-ubuntu \
+ 	lxc-test-unpriv \
+ 	may_control.c \
+diff --git a/src/tests/lxc-test-symlink b/src/tests/lxc-test-symlink
+new file mode 100644
+index 0000000..37320f0
+--- /dev/null
++++ b/src/tests/lxc-test-symlink
+@@ -0,0 +1,88 @@
++#!/bin/bash
++
++set -ex
++
++# lxc: linux Container library
++
++# Authors:
++# Serge Hallyn <serge.hallyn@ubuntu.com>
++#
++# This is a regression test for symbolic links
++
++dirname=`mktemp -d`
++fname=`mktemp`
++fname2=`mktemp`
++
++lxcpath=/var/lib/lxcsym1
++
++cleanup() {
++	lxc-destroy -P $lxcpath -f -n symtest1 || true
++	rm -f $lxcpath
++	rmdir $dirname || true
++	rm -f $fname || true
++	rm -f $fname2 || true
++}
++
++trap cleanup EXIT SIGHUP SIGINT SIGTERM
++
++testrun() {
++	expected=$1
++	run=$2
++	pass="pass"
++	lxc-start -P $lxcpath -n symtest1 -l trace -o $lxcpath/log || pass="fail"
++	[ $pass = "pass" ] && lxc-wait -P $lxcpath -n symtest1 -t 10 -s RUNNING || pass="fail"
++	if [ "$pass" != "$expected" ]; then
++		echo "Test $run: expected $expected but container did not.  Start log:"
++		cat $lxcpath/log
++		echo "FAIL: Test $run: expected $expected but container did not."
++		false
++	fi
++	lxc-stop -P $lxcpath -n symtest1 -k || true
++}
++
++# make lxcpath a symlink - this should NOT cause failure
++ln -s /var/lib/lxc $lxcpath
++
++lxc-destroy -P $lxcpath -f -n symtest1 || true
++lxc-create -P $lxcpath -t busybox -n symtest1
++
++cat >> /var/lib/lxc/symtest1/config << EOF
++lxc.mount.entry = $dirname opt/xxx/dir none bind,create=dir
++lxc.mount.entry = $fname opt/xxx/file none bind,create=file
++lxc.mount.entry = $fname2 opt/xxx/file2 none bind
++EOF
++
++# Regular - should succeed
++mkdir -p /var/lib/lxc/symtest1/rootfs/opt/xxx
++touch /var/lib/lxc/symtest1/rootfs/opt/xxx/file2
++testrun pass 1
++
++# symlink - should fail
++rm -rf /var/lib/lxc/symtest1/rootfs/opt/xxx
++mkdir -p /var/lib/lxc/symtest1/rootfs/opt/xxx2
++ln -s /var/lib/lxc/symtest1/rootfs/opt/xxx2 /var/lib/lxc/symtest1/rootfs/opt/xxx
++touch /var/lib/lxc/symtest1/rootfs/opt/xxx/file2
++testrun fail 2
++
++# final final symlink - should fail
++rm -rf $lxcpath/symtest1/rootfs/opt/xxx
++mkdir -p $lxcpath/symtest1/rootfs/opt/xxx
++mkdir -p $lxcpath/symtest1/rootfs/opt/xxx/dir
++touch $lxcpath/symtest1/rootfs/opt/xxx/file
++touch $lxcpath/symtest1/rootfs/opt/xxx/file2src
++ln -s $lxcpath/symtest1/rootfs/opt/xxx/file2src $lxcpath/symtest1/rootfs/opt/xxx/file2
++testrun fail 3
++
++# Ideally we'd also try a loop device, but that won't work in nested containers
++# anyway - TODO
++
++# what about /proc itself
++
++rm -rf $lxcpath/symtest1/rootfs/opt/xxx
++mkdir -p $lxcpath/symtest1/rootfs/opt/xxx
++touch $lxcpath/symtest1/rootfs/opt/xxx/file2
++mv $lxcpath/symtest1/rootfs/proc $lxcpath/symtest1/rootfs/proc1
++ln -s $lxcpath/symtest1/rootfs/proc1 $lxcpath/symtest1/rootfs/proc
++testrun fail 4
++
++echo "all tests passed"
+-- 
+2.5.0
+