Re: [PATCH v26 11/12] samples/landlock: Add a sandbox manager example
On 14/01/2021 04:21, Jann Horn wrote:
> On Wed, Dec 9, 2020 at 8:29 PM Mickaël Salaün wrote:
>> Add a basic sandbox tool to launch a command which can only access a
>> whitelist of file hierarchies in a read-only or read-write way.
>
> I have to admit that I didn't really look at this closely before
> because it's just sample code... but I guess I should. You can add
>
> Reviewed-by: Jann Horn
>
> if you fix the following nits:
OK, I will!
>
> [...]
>> diff --git a/samples/Kconfig b/samples/Kconfig
> [...]
>> +config SAMPLE_LANDLOCK
>> + bool "Build Landlock sample code"
>> + depends on HEADERS_INSTALL
>> + help
>> + Build a simple Landlock sandbox manager able to launch a process
>> + restricted by a user-defined filesystem access control.
>
> nit: s/filesystem access control/filesystem access control policy/
>
> [...]
>> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> [...]
>> +/*
>> + * Simple Landlock sandbox manager able to launch a process restricted by a
>> + * user-defined filesystem access control.
>
> nit: s/filesystem access control/filesystem access control policy/
>
> [...]
>> +int main(const int argc, char *const argv[], char *const *const envp)
>> +{
> [...]
>> + if (argc < 2) {
> [...]
>> + fprintf(stderr, "* %s: list of paths allowed to be used in a
>> read-only way.\n",
>> + ENV_FS_RO_NAME);
>> + fprintf(stderr, "* %s: list of paths allowed to be used in a
>> read-write way.\n",
>> + ENV_FS_RO_NAME);
>
> s/ENV_FS_RO_NAME/ENV_FS_RW_NAME/
>
>> + fprintf(stderr, "\nexample:\n"
>> +
>> "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
>> +
>> "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
>> + "%s bash -i\n",
>> + ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
>> + return 1;
>> + }
>> +
>> + ruleset_fd = landlock_create_ruleset(_attr,
>> sizeof(ruleset_attr), 0);
>> + if (ruleset_fd < 0) {
>> + perror("Failed to create a ruleset");
>> + switch (errno) {
>
> (Just as a note: In theory perror() can change the value of errno, as
> far as I know - so AFAIK you'd theoretically have to do something
> like:
>
> int errno_ = errno;
> perror("...");
> switch (errno_) {
> ...
> }
Indeed :)
>
> I'll almost certainly work fine as-is in practice though.)
>
Re: [PATCH v26 11/12] samples/landlock: Add a sandbox manager example
On Wed, Dec 9, 2020 at 8:29 PM Mickaël Salaün wrote:
> Add a basic sandbox tool to launch a command which can only access a
> whitelist of file hierarchies in a read-only or read-write way.
I have to admit that I didn't really look at this closely before
because it's just sample code... but I guess I should. You can add
Reviewed-by: Jann Horn
if you fix the following nits:
[...]
> diff --git a/samples/Kconfig b/samples/Kconfig
[...]
> +config SAMPLE_LANDLOCK
> + bool "Build Landlock sample code"
> + depends on HEADERS_INSTALL
> + help
> + Build a simple Landlock sandbox manager able to launch a process
> + restricted by a user-defined filesystem access control.
nit: s/filesystem access control/filesystem access control policy/
[...]
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
[...]
> +/*
> + * Simple Landlock sandbox manager able to launch a process restricted by a
> + * user-defined filesystem access control.
nit: s/filesystem access control/filesystem access control policy/
[...]
> +int main(const int argc, char *const argv[], char *const *const envp)
> +{
[...]
> + if (argc < 2) {
[...]
> + fprintf(stderr, "* %s: list of paths allowed to be used in a
> read-only way.\n",
> + ENV_FS_RO_NAME);
> + fprintf(stderr, "* %s: list of paths allowed to be used in a
> read-write way.\n",
> + ENV_FS_RO_NAME);
s/ENV_FS_RO_NAME/ENV_FS_RW_NAME/
> + fprintf(stderr, "\nexample:\n"
> +
> "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
> +
> "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
> + "%s bash -i\n",
> + ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
> + return 1;
> + }
> +
> + ruleset_fd = landlock_create_ruleset(_attr,
> sizeof(ruleset_attr), 0);
> + if (ruleset_fd < 0) {
> + perror("Failed to create a ruleset");
> + switch (errno) {
(Just as a note: In theory perror() can change the value of errno, as
far as I know - so AFAIK you'd theoretically have to do something
like:
int errno_ = errno;
perror("...");
switch (errno_) {
...
}
I'll almost certainly work fine as-is in practice though.)
[PATCH v26 11/12] samples/landlock: Add a sandbox manager example
From: Mickaël Salaün
Add a basic sandbox tool to launch a command which can only access a
whitelist of file hierarchies in a read-only or read-write way.
Cc: James Morris
Cc: Jann Horn
Cc: Kees Cook
Cc: Serge E. Hallyn
Signed-off-by: Mickaël Salaün
---
Changes since v25:
* Remove useless errno set in the syscall wrappers.
* Cosmetic variable renames.
Changes since v23:
* Re-add hints to help users understand the required kernel
configuration. This was removed with the removal of
landlock_get_features(2).
Changes since v21:
* Remove LANDLOCK_ACCESS_FS_CHROOT.
* Clean up help.
Changes since v20:
* Update with new syscalls and type names.
* Update errno check for EOPNOTSUPP.
* Use the full syscall interfaces: explicitely set the "flags" field to
zero.
Changes since v19:
* Update with the new Landlock syscalls.
* Comply with commit 5f2fb52fac15 ("kbuild: rename hostprogs-y/always to
hostprogs/always-y").
Changes since v16:
* Switch syscall attribute pointer and size arguments.
Changes since v15:
* Update access right names.
* Properly assign access right to files according to the new related
syscall restriction.
* Replace "select" with "depends on" HEADERS_INSTALL (suggested by Randy
Dunlap).
Changes since v14:
* Fix Kconfig dependency.
* Remove access rights that may be required for FD-only requests:
mmap, truncate, getattr, lock, chmod, chown, chgrp, ioctl.
* Fix useless hardcoded syscall number.
* Use execvpe().
* Follow symlinks.
* Extend help with common file paths.
* Constify variables.
* Clean up comments.
* Improve error message.
Changes since v11:
* Add back the filesystem sandbox manager and update it to work with the
new Landlock syscall.
Previous changes:
https://lore.kernel.org/lkml/20190721213116.23476-9-...@digikod.net/
---
samples/Kconfig | 7 ++
samples/Makefile | 1 +
samples/landlock/.gitignore | 1 +
samples/landlock/Makefile| 15 +++
samples/landlock/sandboxer.c | 233 +++
5 files changed, 257 insertions(+)
create mode 100644 samples/landlock/.gitignore
create mode 100644 samples/landlock/Makefile
create mode 100644 samples/landlock/sandboxer.c
diff --git a/samples/Kconfig b/samples/Kconfig
index 0ed6e4d71d87..e6129496ced5 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -124,6 +124,13 @@ config SAMPLE_HIDRAW
bool "hidraw sample"
depends on CC_CAN_LINK && HEADERS_INSTALL
+config SAMPLE_LANDLOCK
+ bool "Build Landlock sample code"
+ depends on HEADERS_INSTALL
+ help
+ Build a simple Landlock sandbox manager able to launch a process
+ restricted by a user-defined filesystem access control.
+
config SAMPLE_PIDFD
bool "pidfd sample"
depends on CC_CAN_LINK && HEADERS_INSTALL
diff --git a/samples/Makefile b/samples/Makefile
index c3392a595e4b..087e0988ccc5 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -11,6 +11,7 @@ obj-$(CONFIG_SAMPLE_KDB) += kdb/
obj-$(CONFIG_SAMPLE_KFIFO) += kfifo/
obj-$(CONFIG_SAMPLE_KOBJECT) += kobject/
obj-$(CONFIG_SAMPLE_KPROBES) += kprobes/
+subdir-$(CONFIG_SAMPLE_LANDLOCK) += landlock
obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch/
subdir-$(CONFIG_SAMPLE_PIDFD) += pidfd
obj-$(CONFIG_SAMPLE_QMI_CLIENT)+= qmi/
diff --git a/samples/landlock/.gitignore b/samples/landlock/.gitignore
new file mode 100644
index ..f43668b2d318
--- /dev/null
+++ b/samples/landlock/.gitignore
@@ -0,0 +1 @@
+/sandboxer
diff --git a/samples/landlock/Makefile b/samples/landlock/Makefile
new file mode 100644
index ..21eda5774948
--- /dev/null
+++ b/samples/landlock/Makefile
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
+hostprogs := sandboxer
+
+always-y := $(hostprogs)
+
+KBUILD_HOSTCFLAGS += -I$(objtree)/usr/include
+
+.PHONY: all clean
+
+all:
+ $(MAKE) -C ../.. samples/landlock/
+
+clean:
+ $(MAKE) -C ../.. M=samples/landlock/ clean
diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
new file mode 100644
index ..82b2738b216c
--- /dev/null
+++ b/samples/landlock/sandboxer.c
@@ -0,0 +1,233 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Simple Landlock sandbox manager able to launch a process restricted by a
+ * user-defined filesystem access control.
+ *
+ * Copyright © 2017-2020 Mickaël Salaün
+ * Copyright © 2020 ANSSI
+ */
+
+#define _GNU_SOURCE
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+#include
+
+#ifndef landlock_create_ruleset
+static inline int landlock_create_ruleset(
+ const struct landlock_ruleset_attr *const attr,
+ const size_t size, const __u32 flags)
+{
+ return syscall(__NR_landlock_create_ruleset, attr, size, flags);
+}
+#endif
+
+#ifndef landlock_add_rule
+static inline int landlock_add_rule(const int
