[RFC PATCH v2 07/21] fuse-bpf: Add support for FUSE_ACCESS

[Daniel Rosenberg <drosen@google.com>]

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 fs/fuse/backing.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 fs/fuse/dir.c     |  6 ++++++
 fs/fuse/fuse_i.h  |  6 ++++++
 3 files changed, 57 insertions(+)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 5a59a8963d52..670e82d68e36 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -390,3 +390,48 @@ int fuse_revalidate_backing(struct dentry *entry, unsigned int flags)
 		return backing_entry->d_op->d_revalidate(backing_entry, flags);
 	return 1;
 }
+
+static int fuse_access_initialize_in(struct fuse_args *fa, struct fuse_access_in *fai,
+				     struct inode *inode, int mask)
+{
+	*fai = (struct fuse_access_in) {
+		.mask = mask,
+	};
+
+	*fa = (struct fuse_args) {
+		.opcode = FUSE_ACCESS,
+		.nodeid = get_node_id(inode),
+		.in_numargs = 1,
+		.in_args[0].size = sizeof(*fai),
+		.in_args[0].value = fai,
+	};
+
+	return 0;
+}
+
+static int fuse_access_initialize_out(struct fuse_args *fa, struct fuse_access_in *fai,
+				      struct inode *inode, int mask)
+{
+	return 0;
+}
+
+static int fuse_access_backing(struct fuse_args *fa, int *out, struct inode *inode, int mask)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	const struct fuse_access_in *fai = fa->in_args[0].value;
+
+	*out = inode_permission(&init_user_ns, fi->backing_inode, fai->mask);
+	return 0;
+}
+
+static int fuse_access_finalize(struct fuse_args *fa, int *out, struct inode *inode, int mask)
+{
+	return 0;
+}
+
+int fuse_bpf_access(int *out, struct inode *inode, int mask)
+{
+	return fuse_bpf_backing(inode, struct fuse_access_in, out,
+				fuse_access_initialize_in, fuse_access_initialize_out,
+				fuse_access_backing, fuse_access_finalize, inode, mask);
+}
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index fb7c6988f0d9..4e19320889ed 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1364,6 +1364,9 @@ static int fuse_access(struct inode *inode, int mask)
 	struct fuse_access_in inarg;
 	int err;
 
+	if (fuse_bpf_access(&err, inode, mask))
+		return err;
+
 	BUG_ON(mask & MAY_NOT_BLOCK);
 
 	if (fm->fc->no_access)
@@ -1420,6 +1423,9 @@ static int fuse_permission(struct user_namespace *mnt_userns,
 	if (!fuse_allow_current_process(fc))
 		return -EACCES;
 
+	if (fuse_bpf_access(&err, inode, mask))
+		return err;
+
 	/*
 	 * If attributes are needed, refresh them before proceeding
 	 */
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 3452530aba94..db3f703c700f 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1401,6 +1401,7 @@ int parse_fuse_bpf_entry(struct fuse_bpf_entry *fbe, int num_entries);
 #ifdef CONFIG_FUSE_BPF
 
 int fuse_bpf_lookup(struct dentry **out, struct inode *dir, struct dentry *entry, unsigned int flags);
+int fuse_bpf_access(int *out, struct inode *inode, int mask);
 
 #else
 
@@ -1409,6 +1410,11 @@ static inline int fuse_bpf_lookup(struct dentry **out, struct inode *dir, struct
 	return 0;
 }
 
+static inline int fuse_bpf_access(int *out, struct inode *inode, int mask)
+{
+	return 0;
+}
+
 #endif // CONFIG_FUSE_BPF
 
 int fuse_handle_backing(struct fuse_bpf_entry *feb, struct path *backing_path);
-- 
2.38.1.584.g0f3c55d4c2-goog