[PATCH v4 0/2] security: add fault injection to LSM hooks

[PATCH v4 0/2] security: add fault injection to LSM hooks

[Aleksandr Nogikh]

From: Aleksandr Nogikh <nogikh@google.com>

Fault injection capabilities[Documentation/fault-injection/fault-injection.rst]
facilitate testing of the stability of the Linux kernel by providing
means to force a number of kernel interfaces to return error
codes. This patch series proposes adding such fault injection
capability into LSM hooks.

The intent is to make it possible to test whether the existing kernel
code properly handles negative return values of LSM hooks. Syzbot
[https://github.com/google/syzkaller/blob/master/docs/syzbot.md] will
automatically do that with the aid of instrumentation tools once these
changes are merged.

Local fuzzing of a Linux kernel with this patch has almost instantly
led to two crashes. I'm not sure whether they correspond to actual
issues as this LSM fault injection implementation (and the concept
itself) can be wrong. Here they are:

1. "general protection fault in selinux_inode_free_security". This is
caused by executing security_inode_free() when a fault was injected to
inode_alloc_security() and therefore selinux_inode_alloc_security()
was not executed. In this case, the subsequent inode_free_security()
call executes list_del_init() on an uninitialized list. Theoretically,
this may happen if some other LSM precedes selinux in the hooks list
and its inode_alloc_security hook fails.

A fault was injected to this call_int_hook():
https://elixir.bootlin.com/linux/v5.9/source/security/security.c#L975

Below you can find a call trace for the subsequent crash.
__list_del_entry include/linux/list.h:132 [inline]
list_del_init include/linux/list.h:204 [inline]
inode_free_security security/selinux/hooks.c:337 [inline]
selinux_inode_free_security+0xf0/0x290 security/selinux/hooks.c:2839
security_inode_free+0x46/0xc0 security/security.c:1042
security_inode_alloc+0x161/0x1a0 security/security.c:1027
inode_init_always+0x5a7/0xd10 fs/inode.c:171
alloc_inode+0x82/0x230 fs/inode.c:239
new_inode_pseudo+0x14/0xe0 fs/inode.c:928
sock_alloc+0x3c/0x260 net/socket.c:573
__sock_create+0xb9/0x780 net/socket.c:1391
sock_create net/socket.c:1478 [inline]
__sys_socket+0xef/0x200 net/socket.c:1520
__do_sys_socket net/socket.c:1529 [inline]
__se_sys_socket net/socket.c:1527 [inline]
__x64_sys_socket+0x6f/0xb0 net/socket.c:1527
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

2. BUG_ON inside security_skb_classify_flow(). Why is it needed there?
https://elixir.bootlin.com/linux/v5.9/source/security/security.c#L2426

---
v4:
* Changed retval debugfs file type - now it stores a signed integer.
* Made CONFIG_FAIL_LSM_HOOKS depend on CONFIG_SECURITY.

v3:
https://lkml.kernel.org/r/20201029183526.2131776-1-aleksandrnogikh@gmail.com
* Submitting this series without an "RFC" tag.
* Updated the cover letter.

v2:
https://lkml.kernel.org/r/20201026125227.54520-1-a.nogikh@gmail.com
* Renamed should_fail_lsm_hook() to lsm_hooks_inject_fail().
* Extended the documentation.

v1:
https://lkml.kernel.org/r/20201015104649.2104432-1-a.nogikh@gmail.com


Aleksandr Nogikh (2):
  security: add fault injection capability
  docs: add fail_lsm_hooks info to fault-injection.rst

 .../fault-injection/fault-injection.rst       |  6 ++
 lib/Kconfig.debug                             |  6 ++
 security/security.c                           | 69 ++++++++++++++++++-
 3 files changed, 78 insertions(+), 3 deletions(-)


base-commit: 3e14f70c05cda4794901ed8f976de3a88deebcc0
-- 
2.29.2.222.g5d2a92d10f8-goog

[PATCH v4 1/2] security: add fault injection capability

[Aleksandr Nogikh]

From: Aleksandr Nogikh <nogikh@google.com>

Add a fault injection capability to call_int_hook macro. This will
facilitate testing of fault tolerance of the code that invokes
security hooks as well as the fault tolerance of the LSM
implementations themselves.

Add a KConfig option (CONFIG_FAIL_LSM_HOOKS) that controls whether the
capability is enabled. In order to enable configuration from the user
space, add the standard debugfs entries for fault injection (if
CONFIG_FAULT_INJECTION_DEBUG_FS is enabled).

Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
---
v4:
- Changed retval debugfs file type - now it keeps a signed integer.
- Made CONFIG_FAIL_LSM_HOOKS depend on CONFIG_SECURITY.
v2:
- Renamed should_fail_lsm_hook() to lsm_hooks_inject_fail().
---
 lib/Kconfig.debug   |  6 ++++
 security/security.c | 69 +++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 72 insertions(+), 3 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 6140413174be..5f4399816019 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1813,6 +1813,12 @@ config FAIL_MAKE_REQUEST
 	help
 	  Provide fault-injection capability for disk IO.
 
+config FAIL_LSM_HOOKS
+	bool "Fault-injection capability for LSM hooks"
+	depends on FAULT_INJECTION && SECURITY
+	help
+	  Provide fault-injection capability for LSM hooks.
+
 config FAIL_IO_TIMEOUT
 	bool "Fault-injection capability for faking disk interrupts"
 	depends on FAULT_INJECTION && BLOCK
diff --git a/security/security.c b/security/security.c
index 69ff6e2e2cd4..be3a3c7c6d6a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -28,6 +28,7 @@
 #include <linux/backing-dev.h>
 #include <linux/string.h>
 #include <linux/msg.h>
+#include <linux/fault-inject.h>
 #include <net/flow.h>
 
 #define MAX_LSM_EVM_XATTR	2
@@ -669,6 +670,67 @@ static void __init lsm_early_task(struct task_struct *task)
 		panic("%s: Early task alloc failed.\n", __func__);
 }
 
+
+#ifdef CONFIG_FAIL_LSM_HOOKS
+
+static struct {
+	struct fault_attr attr;
+	int retval;
+} fail_lsm_hooks = {
+	.attr = FAULT_ATTR_INITIALIZER,
+	.retval = -EACCES
+};
+
+static int __init setup_fail_lsm_hooks(char *str)
+{
+	return setup_fault_attr(&fail_lsm_hooks.attr, str);
+}
+__setup("fail_lsm_hooks=", setup_fail_lsm_hooks);
+
+static int lsm_hooks_inject_fail(void)
+{
+	return should_fail(&fail_lsm_hooks.attr, 1) ? fail_lsm_hooks.retval : 0;
+}
+
+#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
+
+static int fail_lsm_retval_set(void *data, u64 val)
+{
+	fail_lsm_hooks.retval = (int)val;
+	return 0;
+}
+
+static int fail_lsm_retval_get(void *data, u64 *val)
+{
+	*val = (u64)fail_lsm_hooks.retval;
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(fail_lsm_retval_ops, fail_lsm_retval_get,
+						 fail_lsm_retval_set, "%lld\n");
+
+static int __init fail_lsm_hooks_debugfs(void)
+{
+	umode_t mode = S_IFREG | 0600;
+	struct dentry *dir;
+
+	dir = fault_create_debugfs_attr("fail_lsm_hooks", NULL,
+					&fail_lsm_hooks.attr);
+	debugfs_create_file("retval", mode, dir, NULL,
+						&fail_lsm_retval_ops);
+	return 0;
+}
+
+late_initcall(fail_lsm_hooks_debugfs);
+
+#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
+
+#else
+
+static inline int lsm_hooks_inject_fail(void) { return 0; }
+
+#endif /* CONFIG_FAIL_LSM_HOOKS */
+
 /*
  * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
  * can be accessed with:
@@ -707,16 +769,17 @@ static void __init lsm_early_task(struct task_struct *task)
 	} while (0)
 
 #define call_int_hook(FUNC, IRC, ...) ({			\
-	int RC = IRC;						\
-	do {							\
+	int RC = lsm_hooks_inject_fail();			\
+	if (RC == 0) {								\
 		struct security_hook_list *P;			\
+		RC = IRC;								\
 								\
 		hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
 			RC = P->hook.FUNC(__VA_ARGS__);		\
 			if (RC != 0)				\
 				break;				\
 		}						\
-	} while (0);						\
+	}							\
 	RC;							\
 })
 
-- 
2.29.2.222.g5d2a92d10f8-goog

[PATCH v4 2/2] docs: add fail_lsm_hooks info to fault-injection.rst

[Aleksandr Nogikh]

From: Aleksandr Nogikh <nogikh@google.com>

Describe fail_lsm_hooks fault injection capability.

Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
--
v2:
- Added this commit.
---
 Documentation/fault-injection/fault-injection.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentation/fault-injection/fault-injection.rst
index 31ecfe44e5b4..48705adfbc18 100644
--- a/Documentation/fault-injection/fault-injection.rst
+++ b/Documentation/fault-injection/fault-injection.rst
@@ -48,6 +48,12 @@ Available fault injection capabilities
   status code is NVME_SC_INVALID_OPCODE with no retry. The status code and
   retry flag can be set via the debugfs.
 
+- fail_lsm_hooks
+
+  injects failures into LSM hooks. When a fault is injected, actual hooks
+  are not executed and a code from /sys/kernel/debug/fail_lsm_hooks/retval
+  is returned (the default value is -EACCES).
+
 
 Configure fault-injection capabilities behavior
 -----------------------------------------------
-- 
2.29.2.222.g5d2a92d10f8-goog

Re: [PATCH v4 1/2] security: add fault injection capability

[Alexander Potapenko]

On Wed, Nov 11, 2020 at 11:45 AM Aleksandr Nogikh <a.nogikh@gmail.com> wrote:
>
> From: Aleksandr Nogikh <nogikh@google.com>
>
> Add a fault injection capability to call_int_hook macro. This will
> facilitate testing of fault tolerance of the code that invokes
> security hooks as well as the fault tolerance of the LSM
> implementations themselves.
>
> Add a KConfig option (CONFIG_FAIL_LSM_HOOKS) that controls whether the
> capability is enabled. In order to enable configuration from the user
> space, add the standard debugfs entries for fault injection (if
> CONFIG_FAULT_INJECTION_DEBUG_FS is enabled).
>
> Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
> Reviewed-by: Marco Elver <elver@google.com>
> Reviewed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
> v4:
> - Changed retval debugfs file type - now it keeps a signed integer.
> - Made CONFIG_FAIL_LSM_HOOKS depend on CONFIG_SECURITY.
> v2:
> - Renamed should_fail_lsm_hook() to lsm_hooks_inject_fail().
> ---
>  lib/Kconfig.debug   |  6 ++++
>  security/security.c | 69 +++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 72 insertions(+), 3 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 6140413174be..5f4399816019 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1813,6 +1813,12 @@ config FAIL_MAKE_REQUEST
>         help
>           Provide fault-injection capability for disk IO.
>
> +config FAIL_LSM_HOOKS
> +       bool "Fault-injection capability for LSM hooks"
> +       depends on FAULT_INJECTION && SECURITY
> +       help
> +         Provide fault-injection capability for LSM hooks.
> +
>  config FAIL_IO_TIMEOUT
>         bool "Fault-injection capability for faking disk interrupts"
>         depends on FAULT_INJECTION && BLOCK
> diff --git a/security/security.c b/security/security.c
> index 69ff6e2e2cd4..be3a3c7c6d6a 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -28,6 +28,7 @@
>  #include <linux/backing-dev.h>
>  #include <linux/string.h>
>  #include <linux/msg.h>
> +#include <linux/fault-inject.h>
>  #include <net/flow.h>
>
>  #define MAX_LSM_EVM_XATTR      2
> @@ -669,6 +670,67 @@ static void __init lsm_early_task(struct task_struct *task)
>                 panic("%s: Early task alloc failed.\n", __func__);
>  }
>
> +
> +#ifdef CONFIG_FAIL_LSM_HOOKS
> +
> +static struct {
> +       struct fault_attr attr;
> +       int retval;
> +} fail_lsm_hooks = {
> +       .attr = FAULT_ATTR_INITIALIZER,
> +       .retval = -EACCES
> +};
> +
> +static int __init setup_fail_lsm_hooks(char *str)
> +{
> +       return setup_fault_attr(&fail_lsm_hooks.attr, str);
> +}
> +__setup("fail_lsm_hooks=", setup_fail_lsm_hooks);
> +
> +static int lsm_hooks_inject_fail(void)
> +{
> +       return should_fail(&fail_lsm_hooks.attr, 1) ? fail_lsm_hooks.retval : 0;
> +}
> +
> +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> +
> +static int fail_lsm_retval_set(void *data, u64 val)
> +{
> +       fail_lsm_hooks.retval = (int)val;
> +       return 0;
> +}
> +
> +static int fail_lsm_retval_get(void *data, u64 *val)
> +{
> +       *val = (u64)fail_lsm_hooks.retval;
> +       return 0;
> +}
> +
> +DEFINE_DEBUGFS_ATTRIBUTE(fail_lsm_retval_ops, fail_lsm_retval_get,
> +                                                fail_lsm_retval_set, "%lld\n");
> +
> +static int __init fail_lsm_hooks_debugfs(void)
> +{
> +       umode_t mode = S_IFREG | 0600;
> +       struct dentry *dir;
> +
> +       dir = fault_create_debugfs_attr("fail_lsm_hooks", NULL,
> +                                       &fail_lsm_hooks.attr);
> +       debugfs_create_file("retval", mode, dir, NULL,
> +                                               &fail_lsm_retval_ops);
> +       return 0;
> +}
> +
> +late_initcall(fail_lsm_hooks_debugfs);
> +
> +#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
> +
> +#else
> +
> +static inline int lsm_hooks_inject_fail(void) { return 0; }
> +
> +#endif /* CONFIG_FAIL_LSM_HOOKS */
> +
>  /*
>   * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
>   * can be accessed with:
> @@ -707,16 +769,17 @@ static void __init lsm_early_task(struct task_struct *task)
>         } while (0)
>
>  #define call_int_hook(FUNC, IRC, ...) ({                       \
> -       int RC = IRC;                                           \
> -       do {                                                    \
> +       int RC = lsm_hooks_inject_fail();                       \
> +       if (RC == 0) {                                                          \
>                 struct security_hook_list *P;                   \
> +               RC = IRC;                                                               \
>                                                                 \
>                 hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
>                         RC = P->hook.FUNC(__VA_ARGS__);         \
>                         if (RC != 0)                            \
>                                 break;                          \
>                 }                                               \
> -       } while (0);                                            \
> +       }                                                       \
>         RC;                                                     \
>  })
>
> --
> 2.29.2.222.g5d2a92d10f8-goog
>


-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

Re: [PATCH v4 0/2] security: add fault injection to LSM hooks

[Aleksandr Nogikh]

On Wed, 11 Nov 2020 at 13:44, Aleksandr Nogikh <a.nogikh@gmail.com> wrote:
>
> From: Aleksandr Nogikh <nogikh@google.com>
>
> Fault injection capabilities[Documentation/fault-injection/fault-injection.rst]
> facilitate testing of the stability of the Linux kernel by providing
> means to force a number of kernel interfaces to return error
> codes. This patch series proposes adding such fault injection
> capability into LSM hooks.
>
> The intent is to make it possible to test whether the existing kernel
> code properly handles negative return values of LSM hooks. Syzbot
> [https://github.com/google/syzkaller/blob/master/docs/syzbot.md] will
> automatically do that with the aid of instrumentation tools once these
> changes are merged.
[...]

James, can you please take another look at the series? Are there
enough reviewed-bys now?

--
Best Regards,
Aleksandr