if user has lxc.rootfs.path = /some/path/foo, but can't access
some piece of that path, then we'll get an unhelpful "failed to
mount" without any indication of the problem.

At least show that there is a permission problem.
Signed-off-by: Serge Hallyn <shallyn@cisco.com>

coverity: bugfixes

lxccontainer: only attach netns on netdev detach

tools: block using lxc-execute without config file

conf: avoid spawning unnecessary subshells

start: do not unconditionally dup std{in,out,err}

confile: add lxc.proc.* to set proc filesystem 

Signed-off-by: Yifeng Tan <tanyifeng1@huawei.com>

The error_num value doesn't tell us anything since the container hasn't exited.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Starting with commit

    commit c5b93afb
    Author: Li Feng <lifeng68@huawei.com>
    Date:   Mon Jul 10 17:19:52 2017 +0800

        start: dup std{in,out,err} to pty slave

        In the case the container has a console with a valid slave pty file descriptor
        we duplicate std{in,out,err} to the slave file descriptor so console logging
        works correctly. When the container does not have a valid slave pty file
        descriptor for its console and is started daemonized we should dup to
        /dev/null.

        Closes #1646.
Signed-off-by: Li Feng <lifeng68@huawei.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

we made std{err,in,out} a duplicate of the slave file descriptor of the console
if it existed. This meant we also duplicated all of them when we executed
application containers in the foreground even if some std{err,in,out} file
descriptor did not refer to a {p,t}ty. This blocked use cases such as:

    echo foo | lxc-execute -n -- cat

which are very valid and common with application containers but less common
with system containers where we don't have to care about this. So my suggestion
is to unconditionally duplicate std{err,in,out} to the console file descriptor
if we are either running daemonized - this ensures that daemonized application
containers with a single bash shell keep on working - or when we are not
running an application container. In other cases we only duplicate those file
descriptors that actually refer to a {p,t}ty. This logic is similar to what we
do for lxc-attach already.

Refers to #1690.
Closes #2028.
Reported-by: Felix Abecassis <fabecassis@nvidia.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

remove logically dead code
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

free allocated memory
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

check return value of snprintf()
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

remove logically dead code
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

free allocated memory
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

initialize handler
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

remove logically dead code
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

free allocated memory
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

do not pass NULL pointer to chdir()
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

do not unmap prematurely
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

check snprintf() return value
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Detaching network namespaces as an unprivileged user is currently not possible
and attaching to the user namespace will mean we are not allowed to move the
network device into an ancestor network namespace.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

- check for memory allocation failure
- free allocated memory
- cleanup function
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

overlay: fix out-of-bounds copy

Signed-off-by: Jonathan Calmels <jcalmels@nvidia.com>

Moving away from internal symbols we can't do hacks like we currently do in
lxc-start and call internal functions like lxc_conf_init(). This is unsafe
anyway. Instead, we should simply error out if the user didn't give us a
configuration file to use. lxc-start refuses to start in that case already.

Relates to discussion in https://github.com/lxc/go-lxc/pull/96#discussion_r155075560 .
Closes #2023.
Reported-by: Felix Abecassis <fabecassis@nvidia.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

Signed-off-by: Jonathan Calmels <jcalmels@nvidia.com>

start: intelligently use clone() on ns sharing

This also ensures that the new more efficient clone() way of sharing namespaces
is tested.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

When I first solved this problem I went for a fork() + setns() + clone() model.
This works fine but has unnecessary overhead for a couple of reasons:

- doing a full fork() including copying file descriptor table and virtual
  memory
- using pipes to retrieve the pid of the second child (the actual container
  process)

This can all be avoided by being a little smart in how we employ the clone()
syscall:

- using CLONE_VM will let us get rid of using pipes since we can simply write
  to the handler because we share the memory with our parent
- using CLONE_VFORK will also let us get rid of using pipes since the execution
  of the parent is suspended until the child returns
- using CLONE_VM will not cause virtual memory to be copied
- using CLONE_FILES will not cause the file descriptor table to be copied

Note that the intermediate clone() is used with CLONE_VM. Some glibc versions
used to reset the pid/tid to -1 when CLONE_VM was used without CLONE_THREAD.
But since the memory between parent and child is shared on CLONE_VM this would
invalidate the getpid() cache that glibc used to maintain and so getpid() in
the child would return the parent's pid. This is all fixed in newer glibc
versions where the getpid() cache is removed and the pid/tid is not reset
anymore. However, if for whatever reason you - dear commiter - somehow need to
get the pid of the dummy intermediate process for do_share_ns() you need to
call syscall(__NR_getpid) directly. The next lxc_clone() call does not employ
CLONE_VM and will be fine.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

do not double close file descriptor
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

ensure \0-termination
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

free allocated memory
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

remove logically dead code
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

free allocated memory
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

used calculated string length when copying into buffer
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

fix use after free
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>