We allow the user to pass in an additional flag to landlock_create_ruleset
which will make the ruleset operate in "supervise" mode, with a supervisor
attached. We create additional space in the landlock_ruleset_attr
structure to pass the newly created supervisor fd back to user-space.
The intention, while not implemented yet, is that the user-space will read
events from this fd and write responses back to it.
Note: need to investigate if fd clone on fork() is handled correctly, but
should be fine if it shares the struct file. We might also want to let the
user customize the flags on this fd, so that they can request no
O_CLOEXEC.
NOTE: despite this patch having a new uapi, I'm still very open to e.g.
re-using fanotify stuff instead (if that makes sense in the end). This is
just a PoC.
Signed-off-by: Tingmao Wang <m@xxxxxxxxxx>
---
include/uapi/linux/landlock.h | 10 ++++
security/landlock/syscalls.c | 102 +++++++++++++++++++++++++++++-----
2 files changed, 98 insertions(+), 14 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index e1d2c27533b4..7bc1eb4859fb 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -50,6 +50,15 @@ struct landlock_ruleset_attr {
* resources (e.g. IPCs).
*/
__u64 scoped;
+ /**
+ * @supervisor_fd: Placeholder to store the supervisor file
+ * descriptor when %LANDLOCK_CREATE_RULESET_SUPERVISE is set.
+ */
+ __s32 supervisor_fd;
+ /**
+ * @pad: Unused, must be zero.
+ */
+ __u32 pad;
};
/*
@@ -60,6 +69,7 @@ struct landlock_ruleset_attr {
*/
/* clang-format off */
#define LANDLOCK_CREATE_RULESET_VERSION (1U << 0)
+#define LANDLOCK_CREATE_RULESET_SUPERVISE (1U << 1)
/* clang-format on */
/**
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index ead9b68168ad..adf7e77023b5 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -32,6 +32,7 @@
#include "limits.h"
#include "net.h"
#include "ruleset.h"
+#include "supervise.h"
#include "setup.h"
static bool is_initialized(void)
@@ -99,8 +100,10 @@ static void build_check_abi(void)
ruleset_size = sizeof(ruleset_attr.handled_access_fs);
ruleset_size += sizeof(ruleset_attr.handled_access_net);
ruleset_size += sizeof(ruleset_attr.scoped);
+ ruleset_size += sizeof(ruleset_attr.supervisor_fd);
+ ruleset_size += sizeof(ruleset_attr.pad);
BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size);
- BUILD_BUG_ON(sizeof(ruleset_attr) != 24);
+ BUILD_BUG_ON(sizeof(ruleset_attr) != 32);
path_beneath_size = sizeof(path_beneath_attr.allowed_access);
path_beneath_size += sizeof(path_beneath_attr.parent_fd);
@@ -151,16 +154,42 @@ static const struct file_operations ruleset_fops = {
.write = fop_dummy_write,
};
-#define LANDLOCK_ABI_VERSION 6
+static int fop_supervisor_release(struct inode *const inode,
+ struct file *const filp)
+{
+ struct landlock_supervisor *supervisor = filp->private_data;
+
+ landlock_put_supervisor(supervisor);
+ return 0;
+}
+
+static const struct file_operations supervisor_fops = {
+ .release = fop_supervisor_release,
+ /* TODO: read, write, poll, dup */
+ .read = fop_dummy_read,
+ .write = fop_dummy_write,
+};
+
+static int
+landlock_supervisor_open_fd(struct landlock_supervisor *const supervisor,
+ const fmode_t mode)
+{
+ landlock_get_supervisor(supervisor);
+ return anon_inode_getfd("[landlock-supervisor]", &supervisor_fops,
+ supervisor, O_RDWR | O_CLOEXEC);
+}
+
+#define LANDLOCK_ABI_VERSION 7
/**
* sys_landlock_create_ruleset - Create a new ruleset
*
- * @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of
- * the new ruleset.
- * @size: Size of the pointed &struct landlock_ruleset_attr (needed for
- * backward and forward compatibility).
- * @flags: Supported value: %LANDLOCK_CREATE_RULESET_VERSION.
+ * @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of
+ * the new ruleset.
+ * @size: Size of the pointed &struct landlock_ruleset_attr (needed for
+ * backward and forward compatibility).
+ * @flags: Supported value: %LANDLOCK_CREATE_RULESET_VERSION,
+ * %LANDLOCK_CREATE_RULESET_SUPERVISE.
*
* This system call enables to create a new Landlock ruleset, and returns the
* related file descriptor on success.
@@ -172,18 +201,21 @@ static const struct file_operations ruleset_fops = {
* Possible returned errors are:
*
* - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
- * - %EINVAL: unknown @flags, or unknown access, or unknown scope, or too small @size;
+ * - %EINVAL: unknown @flags, or unknown access, or unknown
+ * scope, or too small @size, or non-zero @pad;
* - %E2BIG: @attr or @size inconsistencies;
* - %EFAULT: @attr or @size inconsistencies;
* - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
*/
SYSCALL_DEFINE3(landlock_create_ruleset,
- const struct landlock_ruleset_attr __user *const, attr,
- const size_t, size, const __u32, flags)
+ struct landlock_ruleset_attr __user *const, attr, const size_t,
+ size, const __u32, flags)
{
struct landlock_ruleset_attr ruleset_attr;
struct landlock_ruleset *ruleset;
+ struct landlock_supervisor *supervisor;
int err, ruleset_fd;
+ bool supervise = false;
/* Build-time checks. */
build_check_abi();
@@ -192,10 +224,16 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
return -EOPNOTSUPP;
if (flags) {
- if ((flags == LANDLOCK_CREATE_RULESET_VERSION) && !attr &&
- !size)
+ if (flags == LANDLOCK_CREATE_RULESET_VERSION) {
+ if (attr || size)
+ return -EINVAL;
return LANDLOCK_ABI_VERSION;
- return -EINVAL;
+ }
+ if (flags == LANDLOCK_CREATE_RULESET_SUPERVISE) {
+ supervise = true;
+ } else {
+ return -EINVAL;
+ }
}
/* Copies raw user space buffer. */
@@ -206,6 +244,13 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
if (err)
return err;
+ if (supervise && size < offsetofend(typeof(ruleset_attr), pad))
+ return -EINVAL;
+
+ if (size >= offsetofend(typeof(ruleset_attr), pad) &&
+ ruleset_attr.pad != 0)
+ return -EINVAL;
+
/* Checks content (and 32-bits cast). */
if ((ruleset_attr.handled_access_fs | LANDLOCK_MASK_ACCESS_FS) !=
LANDLOCK_MASK_ACCESS_FS)
@@ -227,11 +272,40 @@ SYSCALL_DEFINE3(landlock_create_ruleset,
if (IS_ERR(ruleset))
return PTR_ERR(ruleset);
+ if (supervise) {
+ supervisor = landlock_create_supervisor();
+ if (IS_ERR(supervisor)) {
+ landlock_put_ruleset(ruleset);
+ return -ENOMEM;
+ }
+ /* Pass ownership of supervisor to ruleset struct */
+ ruleset->layer_stack[0].supervisor = supervisor;
+ }
+
/* Creates anonymous FD referring to the ruleset. */
ruleset_fd = anon_inode_getfd("[landlock-ruleset]", &ruleset_fops,
ruleset, O_RDWR | O_CLOEXEC);
- if (ruleset_fd < 0)
+ if (ruleset_fd < 0) {
landlock_put_ruleset(ruleset);
+ return ruleset_fd;
+ }
+
+ if (supervise) {
+ int supervisor_fd;
+
+ supervisor_fd = landlock_supervisor_open_fd(
+ ruleset->layer_stack[0].supervisor, O_RDWR | O_CLOEXEC);
+ if (supervisor_fd < 0) {
+ landlock_put_ruleset(ruleset);
+ return supervisor_fd;
+ }
+ if (copy_to_user(&attr->supervisor_fd, &supervisor_fd,
+ sizeof(supervisor_fd))) {
+ landlock_put_ruleset(ruleset);
+ return -EFAULT;
+ }
+ }
+
return ruleset_fd;
}
--
2.39.5
