Certain files, when moved to another process have metadata changed, such as netprioidx, and classid. This is the default behaviour in sending sockets with SCM_RIGHTS over unix sockets. Depending on the usecase, this may or may not be desirable with the addfd ioctl. This allows the user to opt-in.
Signed-off-by: Sargun Dhillon <[email protected]> Suggested-by: Tycho Andersen <[email protected]> Cc: Matt Denton <[email protected]> Cc: Kees Cook <[email protected]>, Cc: Jann Horn <[email protected]>, Cc: Robert Sesek <[email protected]>, Cc: Chris Palmer <[email protected]> Cc: Christian Brauner <[email protected]> --- include/uapi/linux/seccomp.h | 8 ++++++++ kernel/seccomp.c | 31 +++++++++++++++++++++++++++---- 2 files changed, 35 insertions(+), 4 deletions(-) diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h index 7d450a9e4c29..ccd1c960372a 100644 --- a/include/uapi/linux/seccomp.h +++ b/include/uapi/linux/seccomp.h @@ -115,6 +115,14 @@ struct seccomp_notif_resp { /* valid flags for seccomp_notif_addfd */ #define SECCOMP_ADDFD_FLAG_SETFD (1UL << 0) /* Specify remote fd */ +/* + * Certain file descriptors are behave differently depending on the process + * they are created in. Specifcally, sockets, and their interactions with the + * net_cls and net_prio cgroup v1 controllers. This "moves" the file descriptor + * so that it takes on the cgroup controller's configuration in the process + * that the file descriptor is being added to. + */ +#define SECCOMP_ADDFD_FLAG_MOVE (1UL << 1) /** * struct seccomp_notif_addfd diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 88940eeabaee..2e649f3cb10e 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -41,6 +41,9 @@ #include <linux/tracehook.h> #include <linux/uaccess.h> #include <linux/anon_inodes.h> +#include <net/netprio_cgroup.h> +#include <net/sock.h> +#include <net/cls_cgroup.h> enum notify_state { SECCOMP_NOTIFY_INIT, @@ -108,6 +111,7 @@ struct seccomp_kaddfd { struct file *file; int fd; unsigned int flags; + bool move; /* To only be set on reply */ int ret; @@ -769,7 +773,8 @@ static u64 seccomp_next_notify_id(struct seccomp_filter *filter) static void seccomp_handle_addfd(struct seccomp_kaddfd *addfd) { - int ret; + struct socket *sock; + int err, ret; /* * Remove the notification, and reset the list pointers, indicating @@ -785,12 +790,29 @@ static void seccomp_handle_addfd(struct seccomp_kaddfd *addfd) ret = replace_fd(addfd->fd, addfd->file, addfd->flags); if (ret >= 0) fput(addfd->file); + else + goto out; } else { ret = get_unused_fd_flags(addfd->flags); if (ret >= 0) fd_install(ret, addfd->file); + else + goto out; } + if (addfd->move) { + sock = sock_from_file(addfd->file, &err); + if (sock) { + sock_update_netprioidx(&sock->sk->sk_cgrp_data); + sock_update_classid(&sock->sk->sk_cgrp_data); + } + } + /* + * An extra reference is taken on the ioctl side, so upon success, we + * must consume all references (and on failure, none). + */ + fput(addfd->file); + out: addfd->ret = ret; complete(&addfd->completion); @@ -1279,16 +1301,17 @@ static long seccomp_notify_addfd(struct seccomp_filter *filter, if (addfd.fd_flags & (~O_CLOEXEC)) return -EINVAL; - if (addfd.flags & ~(SECCOMP_ADDFD_FLAG_SETFD)) + if (addfd.flags & ~(SECCOMP_ADDFD_FLAG_SETFD|SECCOMP_ADDFD_FLAG_MOVE)) return -EINVAL; if (addfd.remote_fd && !(addfd.flags & SECCOMP_ADDFD_FLAG_SETFD)) return -EINVAL; - kaddfd.file = fget(addfd.fd); + kaddfd.file = fget_many(addfd.fd, 2); if (!kaddfd.file) return -EBADF; + kaddfd.move = (addfd.flags & SECCOMP_ADDFD_FLAG_MOVE); kaddfd.flags = addfd.fd_flags; kaddfd.fd = (addfd.flags & SECCOMP_ADDFD_FLAG_SETFD) ? addfd.remote_fd : -1; @@ -1339,7 +1362,7 @@ static long seccomp_notify_addfd(struct seccomp_filter *filter, mutex_unlock(&filter->notify_lock); out: if (ret < 0) - fput(kaddfd.file); + fput_many(kaddfd.file, 2); return ret; } -- 2.25.1
