Subject: [PATCH net-next 4/4] selinux: bpf: Add addtional check for bpf object file receive

From: Chenbo Feng <[email-masked]>
Date: Wed, 4 Oct 2017 11:29:32 -0700

From: Chenbo Feng <[email-masked]>

Introduce a bpf object related check when sending and receiving files
through unix domain socket as well as binder. It checks if the receiving
process have privilege to read/write the bpf map or use the bpf program.
This check is necessary because the bpf maps and programs are using a
anonymous inode as their shared inode so the normal way of checking the
files and sockets when passing between processes cannot work properly on
eBPF object. This check only works when the BPF_SYSCALL is configured.

Signed-off-by: Chenbo Feng <[email-masked]>
---
 include/linux/bpf.h      |  3 +++
 kernel/bpf/syscall.c     |  4 ++--
 security/selinux/hooks.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index d757ea3f2228..ac8428a36d56 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -250,6 +250,9 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 #ifdef CONFIG_BPF_SYSCALL
 DECLARE_PER_CPU(int, bpf_prog_active);
 
+extern const struct file_operations bpf_map_fops;
+extern const struct file_operations bpf_prog_fops;
+
 #define BPF_PROG_TYPE(_id, _ops) \
 	extern const struct bpf_verifier_ops _ops;
 #define BPF_MAP_TYPE(_id, _ops) \
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 58ff769d58ab..5789a5359f0a 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -313,7 +313,7 @@ static ssize_t bpf_dummy_write(struct file *filp, const char __user *buf,
 	return -EINVAL;
 }
 
-static const struct file_operations bpf_map_fops = {
+const struct file_operations bpf_map_fops = {
 #ifdef CONFIG_PROC_FS
 	.show_fdinfo	= bpf_map_show_fdinfo,
 #endif
@@ -965,7 +965,7 @@ static void bpf_prog_show_fdinfo(struct seq_file *m, struct file *filp)
 }
 #endif
 
-static const struct file_operations bpf_prog_fops = {
+const struct file_operations bpf_prog_fops = {
 #ifdef CONFIG_PROC_FS
 	.show_fdinfo	= bpf_prog_show_fdinfo,
 #endif
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 41aba4e3d57c..381474ce3216 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1847,6 +1847,7 @@ static int file_has_perm(const struct cred *cred,
 
 	/* av is zero if only checking access to the descriptor. */
 	rc = 0;
+
 	if (av)
 		rc = inode_has_perm(cred, inode, av, &ad);
 
@@ -2142,6 +2143,10 @@ static int selinux_binder_transfer_binder(struct task_struct *from,
 			    NULL);
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+static int bpf_fd_pass(struct file *file, u32 sid);
+#endif
+
 static int selinux_binder_transfer_file(struct task_struct *from,
 					struct task_struct *to,
 					struct file *file)
@@ -2165,6 +2170,12 @@ static int selinux_binder_transfer_file(struct task_struct *from,
 			return rc;
 	}
 
+#ifdef CONFIG_BPF_SYSCALL
+	rc = bpf_fd_pass(file, sid);
+	if (rc)
+		return rc;
+#endif
+
 	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
 		return 0;
 
@@ -3735,8 +3746,18 @@ static int selinux_file_send_sigiotask(struct task_struct *tsk,
 static int selinux_file_receive(struct file *file)
 {
 	const struct cred *cred = current_cred();
+	int rc;
+
+	rc = file_has_perm(cred, file, file_to_av(file));
+	if (rc)
+		goto out;
+
+#ifdef CONFIG_BPF_SYSCALL
+	rc = bpf_fd_pass(file, cred_sid(sid));
+#endif
 
-	return file_has_perm(cred, file, file_to_av(file));
+out:
+	return rc;
 }
 
 static int selinux_file_open(struct file *file, const struct cred *cred)
@@ -6288,6 +6309,40 @@ static u32 bpf_map_fmode_to_av(fmode_t fmode)
 	return av;
 }
 
+/* This function will check the file pass through unix socket or binder to see
+ * if it is a bpf related object. And apply correspinding checks on the bpf
+ * object based on the type. The bpf maps and programs, not like other files and
+ * socket, are using a shared anonymous inode inside the kernel as their inode.
+ * So checking that inode cannot identify if the process have privilege to
+ * access the bpf object and that's why we have to add this additional check in
+ * selinux_file_receive and selinux_binder_transfer_files.
+ */
+static int bpf_fd_pass(struct file *file, u32 sid)
+{
+	struct bpf_security_struct *bpfsec;
+	u32 sid = cred_sid(cred);
+	struct bpf_prog *prog;
+	struct bpf_map *map;
+	int ret;
+
+	if (file->f_op == &bpf_map_fops) {
+		map = file->private_data;
+		bpfsec = map->security;
+		ret = avc_has_perm(sid, bpfsec->sid, SECCLASS_BPF_MAP,
+				   bpf_map_fmode_to_av(file->f_mode), NULL);
+		if (ret)
+			return ret;
+	} else if (file->f_op == &bpf_prog_fops) {
+		prog = file->private_data;
+		bpfsec = prog->aux->security;
+		ret = avc_has_perm(sid, bpfsec->sid, SECCLASS_BPF_PROG,
+				   BPF_PROG__USE, NULL);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
 static int selinux_bpf_map(struct bpf_map *map, fmode_t fmode)
 {
 	u32 sid = current_sid();
-- 
2.14.2.920.gcf0c67979c-goog