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Date: Thu, 28 Mar 2024 18:53:22 -0700
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Subject: [RFC PATCH v4 07/36] fuse-bpf: Add support for access
From: Daniel Rosenberg <drosen@google.com>
To: Miklos Szeredi <miklos@szeredi.hu>, bpf@vger.kernel.org, 
	Alexei Starovoitov <ast@kernel.org>
Cc: Amir Goldstein <amir73il@gmail.com>, linux-kernel@vger.kernel.org, 
	linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, 
	Daniel Borkmann <daniel@iogearbox.net>, John Fastabend <john.fastabend@gmail.com>, 
	Andrii Nakryiko <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, Song Liu <song@kernel.org>, 
	Eduard Zingerman <eddyz87@gmail.com>, Yonghong Song <yonghong.song@linux.dev>, 
	KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
	Jiri Olsa <jolsa@kernel.org>, Shuah Khan <shuah@kernel.org>, Jonathan Corbet <corbet@lwn.net>, 
	Joanne Koong <joannelkoong@gmail.com>, Mykola Lysenko <mykolal@fb.com>, 
	Christian Brauner <brauner@kernel.org>, kernel-team@android.com, 
	Daniel Rosenberg <drosen@google.com>, Paul Lawrence <paullawrence@google.com>
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This adds backing support for FUSE_ACCESS

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 fs/fuse/backing.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 fs/fuse/dir.c     |  6 ++++++
 fs/fuse/fuse_i.h  |  6 ++++++
 3 files changed, 59 insertions(+)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 14fcc2032764..a94d99ff9862 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -420,3 +420,50 @@ 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 bpf_fuse_args *fa, struct fuse_access_in *in,
+				     struct inode *inode, int mask)
+{
+	*in = (struct fuse_access_in) {
+		.mask = mask,
+	};
+
+	*fa = (struct bpf_fuse_args) {
+		.info = (struct bpf_fuse_meta_info) {
+			.opcode = FUSE_ACCESS,
+			.nodeid = get_node_id(inode),
+		},
+		.in_numargs = 1,
+		.in_args[0].size = sizeof(*in),
+		.in_args[0].value = in,
+	};
+
+	return 0;
+}
+
+static int fuse_access_initialize_out(struct bpf_fuse_args *fa, struct fuse_access_in *in,
+				      struct inode *inode, int mask)
+{
+	return 0;
+}
+
+static int fuse_access_backing(struct bpf_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(&nop_mnt_idmap, fi->backing_inode, fai->mask);
+	return 0;
+}
+
+static int fuse_access_finalize(struct bpf_fuse_args *fa, int *out, struct inode *inode, int mask)
+{
+	return 0;
+}
+
+int fuse_bpf_access(int *out, struct inode *inode, int mask)
+{
+	return bpf_fuse_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 6503c91886f6..8db6eb6a0848 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1563,6 +1563,9 @@ 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)
@@ -1619,6 +1622,9 @@ static int fuse_permission(struct mnt_idmap *idmap,
 	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 dd62e78e474c..08ee98b7bb95 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1439,6 +1439,7 @@ 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
 
@@ -1447,6 +1448,11 @@ 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);
-- 
2.44.0.478.gd926399ef9-goog