bpf, inode: allow for rename and link ops

Add support for renaming and hard links to the fs. Most of this can be
implemented by using simple library operations under the same constraints
that we don't use a reserved name like elsewhere. Linking can be useful
to share/manage things like maps across subsystem users. It works within
the file system boundary, but is not allowed for directories.

Symbolic links are explicitly not implemented here, as it can be better
done already by doing bind mounts inside bpf fs to set up shared directories
f.e. useful when using volumes in docker containers that map a private
working directory into /sys/fs/bpf/ which contains itself a bind mounted
path from the host's /sys/fs/bpf/ mount that is shared among multiple
containers. For single maps instead of whole directory, hard links can
be easily used to do the same.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 5a8a797d50b74a8bb698760856c1849ff9bcc084..f2ece3c174a5b540b40492833048d6c8bd9f3f1c 100644 (file)
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -187,11 +187,31 @@ static int bpf_mkobj(struct inode *dir, struct dentry *dentry, umode_t mode,
        }
 }
 
+static int bpf_link(struct dentry *old_dentry, struct inode *dir,
+                   struct dentry *new_dentry)
+{
+       if (bpf_dname_reserved(new_dentry))
+               return -EPERM;
+
+       return simple_link(old_dentry, dir, new_dentry);
+}
+
+static int bpf_rename(struct inode *old_dir, struct dentry *old_dentry,
+                     struct inode *new_dir, struct dentry *new_dentry)
+{
+       if (bpf_dname_reserved(new_dentry))
+               return -EPERM;
+
+       return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
+}
+
 static const struct inode_operations bpf_dir_iops = {
        .lookup         = simple_lookup,
        .mknod          = bpf_mkobj,
        .mkdir          = bpf_mkdir,
        .rmdir          = simple_rmdir,
+       .rename         = bpf_rename,
+       .link           = bpf_link,
        .unlink         = simple_unlink,
 };