netdev - [WIP 2/4] bpf: Don't require mknod() permission to pin an object

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Date:   Mon,  5 Aug 2019 14:29:03 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Song Liu <songliubraving@...com>,
        Kees Cook <keescook@...omium.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Jann Horn <jannh@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [WIP 2/4] bpf: Don't require mknod() permission to pin an object

security_path_mknod() seems excessive for pinning an object --
pinning an object is effectively just creating a file.  It's also
redundant, as vfs_mkobj() calls security_inode_create() by itself.

This isn't strictly required -- mknod(path, S_IFREG, unused) works
to create regular files, but bpf is currently the only user in the
kernel outside of mknod() itself that uses it to create regular
(i.e. S_IFREG) files.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 kernel/bpf/inode.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index cb07736b33ae..14304609003a 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -394,10 +394,6 @@ static int bpf_obj_do_pin(const struct filename *pathname, void *raw,
 
 	mode = S_IFREG | ((S_IRUSR | S_IWUSR) & ~current_umask());
 
-	ret = security_path_mknod(&path, dentry, mode, 0);
-	if (ret)
-		goto out;
-
 	dir = d_inode(path.dentry);
 	if (dir->i_op != &bpf_dir_iops) {
 		ret = -EPERM;
-- 
2.21.0