[PATCH net-next v6 5/5] selinux: bpf: Add addtional check for bpf object file receive

[chenbofeng.kernel@gmail.com (Chenbo Feng)]

From: Chenbo Feng <fengc@google.com>

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 <fengc@google.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
---
 include/linux/bpf.h      |  3 +++
 kernel/bpf/syscall.c     |  4 ++--
 security/selinux/hooks.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 1479442d5293..1ac507dc19a8 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -285,6 +285,9 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs,
 #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 d3e152e282d8..8bdb98aa7f34 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
@@ -967,7 +967,7 @@ 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 12cf7de8cbed..2e3a627fc0b1 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1815,6 +1815,10 @@ static inline int file_path_has_perm(const struct cred *cred,
 	return inode_has_perm(cred, file_inode(file), av, &ad);
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+static int bpf_fd_pass(struct file *file, u32 sid);
+#endif
+
 /* Check whether a task can use an open file descriptor to
    access an inode in a given way.  Check access to the
    descriptor itself, and then use dentry_has_perm to
@@ -1845,6 +1849,12 @@ static int file_has_perm(const struct cred *cred,
 			goto out;
 	}
 
+#ifdef CONFIG_BPF_SYSCALL
+	rc = bpf_fd_pass(file, cred_sid(cred));
+	if (rc)
+		return rc;
+#endif
+
 	/* av is zero if only checking access to the descriptor. */
 	rc = 0;
 	if (av)
@@ -2165,6 +2175,12 @@ 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;
 
@@ -6288,6 +6304,39 @@ 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;
+	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,
+				   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,
+				   BPF__PROG_RUN, NULL);
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
 static int selinux_bpf_map(struct bpf_map *map, fmode_t fmode)
 {
 	u32 sid = current_sid();
-- 
2.15.0.rc0.271.g36b669edcc-goog

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