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 <sargun@xxxxxxxxx>
Suggested-by: Tycho Andersen <tycho@xxxxxxxx>
Cc: Matt Denton <mpdenton@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>,
Cc: Jann Horn <jannh@xxxxxxxxxx>,
Cc: Robert Sesek <rsesek@xxxxxxxxxx>,
Cc: Chris Palmer <palmer@xxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
---
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
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