Re: [PATCH 2/2] virtiofsd: move to a new pid namespace
On Thu, Oct 24, 2019 at 11:26:11AM +0100, Daniel P. Berrangé wrote: > On Wed, Oct 16, 2019 at 05:01:57PM +0100, Stefan Hajnoczi wrote: > It might be useful to call prctl(PR_SET_PDEATHSIG) here, so that > if the parent process exits for any reason, the child will be killed > off too. [...] > I feel like this is making things a bit misleading. > > setup_pid_namespace() > > is now creating the mount namespace and pid namespace, and doing > some mount point config > > setup_mount_namespace() > > is not creating the mount namespace, but is doing some more mount > point config. > > And then there's setup_net_namespace() too. > > I think there could be a single > > setup_namespaces() > > method that does the unshare(CLONE_NEWNS|CLONE_NEWNET|CLONE_NEWPID) > and forking the child. > > And a setup_mounts() > > method that does all the mount() calls. Thanks for your suggestions. I'll implement both of them as follow-up patches since this has already been included in the virtiofsd code. Stefan signature.asc Description: PGP signature
Re: [PATCH 2/2] virtiofsd: move to a new pid namespace
On Wed, Oct 16, 2019 at 05:01:57PM +0100, Stefan Hajnoczi wrote:
> virtiofsd needs access to /proc/self/fd. Let's move to a new pid
> namespace so that a compromised process cannot see another other
> processes running on the system.
>
> One wrinkle in this approach: unshare(CLONE_NEWPID) affects *child*
> processes and not the current process. Therefore we need to fork the
> pid 1 process that will actually run virtiofsd and leave a parent in
> waitpid(2). This is not the same thing as daemonization and parent
> processes should not notice a difference.
>
> Signed-off-by: Stefan Hajnoczi
> ---
> contrib/virtiofsd/passthrough_ll.c | 95 ++
> 1 file changed, 72 insertions(+), 23 deletions(-)
>
> diff --git a/contrib/virtiofsd/passthrough_ll.c
> b/contrib/virtiofsd/passthrough_ll.c
> index c27ff7d800..b6ee9b2e90 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -56,9 +56,12 @@
> #include
> #include
> #include
> +#include
> #include
> +#include
> #include
>
> +
> #include "ireg.h"
> #include
> #include
> @@ -2749,6 +2752,72 @@ static void setup_net_namespace(void)
> }
> }
>
> +/*
> + * Move to a new pid namespace to prevent access to other processes if this
> + * process is compromised.
> + */
> +static void setup_pid_namespace(void)
> +{
> + pid_t child;
> +
> + /*
> + * Create a new pid namespace for *child* processes. We'll have to
> + * fork in order to enter the new pid namespace. A new mount namespace
> + * is also needed so that we can remount /proc for the new pid
> + * namespace.
> + */
> + if (unshare(CLONE_NEWPID | CLONE_NEWNS) != 0) {
> + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWPID | CLONE_NEWNS):
> %m\n");
> + exit(1);
> + }
> +
> + child = fork();
> + if (child < 0) {
> + fuse_log(FUSE_LOG_ERR, "fork() failed: %m\n");
> + exit(1);
> + }
> + if (child > 0) {
> + pid_t waited;
> + int wstatus;
> +
> + /* The parent waits for the child */
> + do {
> + waited = waitpid(child, , 0);
> + } while (waited < 0 && errno == EINTR);
> +
> + if (WIFEXITED(wstatus)) {
> + exit(WEXITSTATUS(wstatus));
> + }
> +
> + exit(1);
> + }
It might be useful to call prctl(PR_SET_PDEATHSIG) here, so that
if the parent process exits for any reason, the child will be killed
off too.
> +
> + /*
> + * If the mounts have shared propagation then we want to opt out so our
> + * mount changes don't affect the parent mount namespace.
> + */
> + if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
> + fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_SLAVE): %m\n");
> + exit(1);
> + }
> +
> + /* The child must remount /proc to use the new pid namespace */
> + if (mount("proc", "/proc", "proc",
> + MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, NULL) < 0) {
> + fuse_log(FUSE_LOG_ERR, "mount(/proc): %m\n");
> + exit(1);
> + }
> +}
I feel like this is making things a bit misleading.
setup_pid_namespace()
is now creating the mount namespace and pid namespace, and doing
some mount point config
setup_mount_namespace()
is not creating the mount namespace, but is doing some more mount
point config.
And then there's setup_net_namespace() too.
I think there could be a single
setup_namespaces()
method that does the unshare(CLONE_NEWNS|CLONE_NEWNET|CLONE_NEWPID)
and forking the child.
And a setup_mounts()
method that does all the mount() calls.
> +
> +static void setup_proc_self_fd(struct lo_data *lo)
> +{
> + lo->proc_self_fd = open("/proc/self/fd", O_PATH);
> + if (lo->proc_self_fd == -1) {
> + fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
> + exit(1);
> + }
> +}
> +
> /* This magic is based on lxc's lxc_pivot_root() */
> static void setup_pivot_root(const char *source)
> {
> @@ -2803,20 +2872,10 @@ static void setup_pivot_root(const char *source)
>
> /*
> * Make the source directory our root so symlinks cannot escape and no other
> - * files are accessible.
> + * files are accessible. Assumes unshare(CLONE_NEWNS) was already called.
> */
> static void setup_mount_namespace(const char *source)
> {
> - if (unshare(CLONE_NEWNS) != 0) {
> - fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWNS): %m\n");
> - exit(1);
> - }
> -
> - if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
> - fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_PRIVATE): %m\n");
> - exit(1);
> - }
> -
> if (mount(source, source, NULL, MS_BIND, NULL) < 0) {
> fuse_log(FUSE_LOG_ERR, "mount(%s, %s, MS_BIND): %m\n", source,
> source);
> exit(1);
> @@
Re: [PATCH 2/2] virtiofsd: move to a new pid namespace
* Stefan Hajnoczi (stefa...@redhat.com) wrote:
> virtiofsd needs access to /proc/self/fd. Let's move to a new pid
> namespace so that a compromised process cannot see another other
> processes running on the system.
>
> One wrinkle in this approach: unshare(CLONE_NEWPID) affects *child*
> processes and not the current process. Therefore we need to fork the
> pid 1 process that will actually run virtiofsd and leave a parent in
> waitpid(2). This is not the same thing as daemonization and parent
> processes should not notice a difference.
>
> Signed-off-by: Stefan Hajnoczi
OK, I think that's OK (I don't know the mount semantics that well).
Reviewed-by: Dr. David Alan Gilbert
> ---
> contrib/virtiofsd/passthrough_ll.c | 95 ++
> 1 file changed, 72 insertions(+), 23 deletions(-)
>
> diff --git a/contrib/virtiofsd/passthrough_ll.c
> b/contrib/virtiofsd/passthrough_ll.c
> index c27ff7d800..b6ee9b2e90 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -56,9 +56,12 @@
> #include
> #include
> #include
> +#include
> #include
> +#include
> #include
>
> +
> #include "ireg.h"
> #include
> #include
> @@ -2749,6 +2752,72 @@ static void setup_net_namespace(void)
> }
> }
>
> +/*
> + * Move to a new pid namespace to prevent access to other processes if this
> + * process is compromised.
> + */
> +static void setup_pid_namespace(void)
> +{
> + pid_t child;
> +
> + /*
> + * Create a new pid namespace for *child* processes. We'll have to
> + * fork in order to enter the new pid namespace. A new mount namespace
> + * is also needed so that we can remount /proc for the new pid
> + * namespace.
> + */
> + if (unshare(CLONE_NEWPID | CLONE_NEWNS) != 0) {
> + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWPID | CLONE_NEWNS):
> %m\n");
> + exit(1);
> + }
> +
> + child = fork();
> + if (child < 0) {
> + fuse_log(FUSE_LOG_ERR, "fork() failed: %m\n");
> + exit(1);
> + }
> + if (child > 0) {
> + pid_t waited;
> + int wstatus;
> +
> + /* The parent waits for the child */
> + do {
> + waited = waitpid(child, , 0);
> + } while (waited < 0 && errno == EINTR);
> +
> + if (WIFEXITED(wstatus)) {
> + exit(WEXITSTATUS(wstatus));
> + }
> +
> + exit(1);
> + }
> +
> + /*
> + * If the mounts have shared propagation then we want to opt out so our
> + * mount changes don't affect the parent mount namespace.
> + */
> + if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
> + fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_SLAVE): %m\n");
> + exit(1);
> + }
> +
> + /* The child must remount /proc to use the new pid namespace */
> + if (mount("proc", "/proc", "proc",
> + MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RELATIME, NULL) < 0) {
> + fuse_log(FUSE_LOG_ERR, "mount(/proc): %m\n");
> + exit(1);
> + }
> +}
> +
> +static void setup_proc_self_fd(struct lo_data *lo)
> +{
> + lo->proc_self_fd = open("/proc/self/fd", O_PATH);
> + if (lo->proc_self_fd == -1) {
> + fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");
> + exit(1);
> + }
> +}
> +
> /* This magic is based on lxc's lxc_pivot_root() */
> static void setup_pivot_root(const char *source)
> {
> @@ -2803,20 +2872,10 @@ static void setup_pivot_root(const char *source)
>
> /*
> * Make the source directory our root so symlinks cannot escape and no other
> - * files are accessible.
> + * files are accessible. Assumes unshare(CLONE_NEWNS) was already called.
> */
> static void setup_mount_namespace(const char *source)
> {
> - if (unshare(CLONE_NEWNS) != 0) {
> - fuse_log(FUSE_LOG_ERR, "unshare(CLONE_NEWNS): %m\n");
> - exit(1);
> - }
> -
> - if (mount(NULL, "/", NULL, MS_REC|MS_SLAVE, NULL) < 0) {
> - fuse_log(FUSE_LOG_ERR, "mount(/, MS_REC|MS_PRIVATE): %m\n");
> - exit(1);
> - }
> -
> if (mount(source, source, NULL, MS_BIND, NULL) < 0) {
> fuse_log(FUSE_LOG_ERR, "mount(%s, %s, MS_BIND): %m\n", source,
> source);
> exit(1);
> @@ -2831,6 +2890,8 @@ static void setup_mount_namespace(const char *source)
> */
> static void setup_sandbox(struct lo_data *lo, bool enable_syslog)
> {
> + setup_pid_namespace();
> + setup_proc_self_fd(lo);
> setup_net_namespace();
> setup_mount_namespace(lo->source);
> setup_seccomp(enable_syslog);
> @@ -2860,15 +2921,6 @@ static void setup_root(struct lo_data *lo, struct
> lo_inode *root)
> g_atomic_int_set(>refcount, 2);
> }
>
> -static void setup_proc_self_fd(struct lo_data *lo)
> -{
> - lo->proc_self_fd = open("/proc/self/fd", O_PATH);
>
