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From: Paul Moore <paul@paul-moore.com>
To: linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	linux-audit@redhat.com, io-uring@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
	Pavel Begunkov <asml.silence@gmail.com>,
	Kumar Kartikeya Dwivedi <memxor@gmail.com>
Subject: [PATCH v3 7/8] selinux: add support for the io_uring access controls
Date: Mon, 13 Sep 2021 23:33:35 -0400	[thread overview]
Message-ID: <163159041500.470089.11310853524829799938.stgit@olly> (raw)
In-Reply-To: <163159032713.470089.11728103630366176255.stgit@olly>

This patch implements two new io_uring access controls, specifically
support for controlling the io_uring "personalities" and
IORING_SETUP_SQPOLL.  Controlling the sharing of io_urings themselves
is handled via the normal file/inode labeling and sharing mechanisms.

The io_uring { override_creds } permission restricts which domains
the subject domain can use to override it's own credentials.
Granting a domain the io_uring { override_creds } permission allows
it to impersonate another domain in io_uring operations.

The io_uring { sqpoll } permission restricts which domains can create
asynchronous io_uring polling threads.  This is important from a
security perspective as operations queued by this asynchronous thread
inherit the credentials of the thread creator by default; if an
io_uring is shared across process/domain boundaries this could result
in one domain impersonating another.  Controlling the creation of
sqpoll threads, and the sharing of io_urings across processes, allow
policy authors to restrict the ability of one domain to impersonate
another via io_uring.

As a quick summary, this patch adds a new object class with two
permissions:

 io_uring { override_creds sqpoll }

These permissions can be seen in the two simple policy statements
below:

  allow domA_t domB_t : io_uring { override_creds };
  allow domA_t self : io_uring { sqpoll };

Signed-off-by: Paul Moore <paul@paul-moore.com>

---
v3:
- removed work-in-progress warning from the description
v2:
- made the selinux_uring_* funcs static
- removed the debugging code
v1:
- initial draft
---
 security/selinux/hooks.c            |   34 ++++++++++++++++++++++++++++++++++
 security/selinux/include/classmap.h |    2 ++
 2 files changed, 36 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 6517f221d52c..012e8504ed9e 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7111,6 +7111,35 @@ static int selinux_perf_event_write(struct perf_event *event)
 }
 #endif
 
+#ifdef CONFIG_IO_URING
+/**
+ * selinux_uring_override_creds - check the requested cred override
+ * @new: the target creds
+ *
+ * Check to see if the current task is allowed to override it's credentials
+ * to service an io_uring operation.
+ */
+static int selinux_uring_override_creds(const struct cred *new)
+{
+	return avc_has_perm(&selinux_state, current_sid(), cred_sid(new),
+			    SECCLASS_IO_URING, IO_URING__OVERRIDE_CREDS, NULL);
+}
+
+/**
+ * selinux_uring_sqpoll - check if a io_uring polling thread can be created
+ *
+ * Check to see if the current task is allowed to create a new io_uring
+ * kernel polling thread.
+ */
+static int selinux_uring_sqpoll(void)
+{
+	int sid = current_sid();
+
+	return avc_has_perm(&selinux_state, sid, sid,
+			    SECCLASS_IO_URING, IO_URING__SQPOLL, NULL);
+}
+#endif /* CONFIG_IO_URING */
+
 /*
  * IMPORTANT NOTE: When adding new hooks, please be careful to keep this order:
  * 1. any hooks that don't belong to (2.) or (3.) below,
@@ -7349,6 +7378,11 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(perf_event_write, selinux_perf_event_write),
 #endif
 
+#ifdef CONFIG_IO_URING
+	LSM_HOOK_INIT(uring_override_creds, selinux_uring_override_creds),
+	LSM_HOOK_INIT(uring_sqpoll, selinux_uring_sqpoll),
+#endif
+
 	LSM_HOOK_INIT(locked_down, selinux_lockdown),
 
 	/*
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 084757ff4390..698ccfdaf82d 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -254,6 +254,8 @@ struct security_class_mapping secclass_map[] = {
 	  { "integrity", "confidentiality", NULL } },
 	{ "anon_inode",
 	  { COMMON_FILE_PERMS, NULL } },
+	{ "io_uring",
+	  { "override_creds", "sqpoll", NULL } },
 	{ NULL }
   };
 


  parent reply	other threads:[~2021-09-14  3:33 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14  3:32 [PATCH v3 0/8] Add LSM access controls and auditing to io_uring Paul Moore
2021-09-14  3:32 ` [PATCH v3 1/8] audit: prepare audit_context for use in calling contexts beyond syscalls Paul Moore
2021-09-14  3:33 ` [PATCH v3 2/8] audit,io_uring,io-wq: add some basic audit support to io_uring Paul Moore
2021-09-14  3:33 ` [PATCH v3 3/8] audit: add filtering for io_uring records Paul Moore
2021-09-14  3:33 ` [PATCH v3 4/8] fs: add anon_inode_getfile_secure() similar to anon_inode_getfd_secure() Paul Moore
2021-09-14  3:33 ` [PATCH v3 5/8] io_uring: convert io_uring to the secure anon inode interface Paul Moore
2021-09-14  3:33 ` [PATCH v3 6/8] lsm,io_uring: add LSM hooks to io_uring Paul Moore
2021-09-14  3:33 ` Paul Moore [this message]
2021-09-14  3:33 ` [PATCH v3 8/8] Smack: Brutalist io_uring support with debug Paul Moore

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