[bpf-next,1/4] bpf/crib: Introduce task_file open-coded iterator kfuncs

Commit Message

Juntong Deng Oct. 29, 2024, 10:39 p.m. UTC

This patch adds the open-coded iterator style process file iterator
kfuncs bpf_iter_task_file_{new,next,destroy} that iterates over all
files opened by the specified process.

In addition, this patch adds bpf_iter_task_file_get_fd() getter to get
the file descriptor corresponding to the file in the current iteration.

The reference to struct file acquired by the previous
bpf_iter_task_file_next() is released in the next
bpf_iter_task_file_next(), and the last reference is released in the
last bpf_iter_task_file_next() that returns NULL.

In the bpf_iter_task_file_destroy(), if the iterator does not iterate to
the end, then the last struct file reference is released at this time.

Signed-off-by: Juntong Deng <[e-mail]>
---
 kernel/bpf/Makefile      |   1 +
 kernel/bpf/crib/Makefile |   3 ++
 kernel/bpf/crib/crib.c   |  29 +++++++++++
 kernel/bpf/crib/files.c  | 105 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 138 insertions(+)
 create mode 100644 kernel/bpf/crib/Makefile
 create mode 100644 kernel/bpf/crib/crib.c
 create mode 100644 kernel/bpf/crib/files.c

Patch

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 105328f0b9c0..933d36264e5e 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -53,3 +53,4 @@  obj-$(CONFIG_BPF_SYSCALL) += relo_core.o
 obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o
 obj-$(CONFIG_BPF_SYSCALL) += kmem_cache_iter.o
+obj-$(CONFIG_BPF_SYSCALL) += crib/
diff --git a/kernel/bpf/crib/Makefile b/kernel/bpf/crib/Makefile
new file mode 100644
index 000000000000..4e1bae1972dd
--- /dev/null
+++ b/kernel/bpf/crib/Makefile
@@ -0,0 +1,3 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_BPF_SYSCALL) += crib.o files.o
diff --git a/kernel/bpf/crib/crib.c b/kernel/bpf/crib/crib.c
new file mode 100644
index 000000000000..e6536ee9a845
--- /dev/null
+++ b/kernel/bpf/crib/crib.c
@@ -0,0 +1,29 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Checkpoint/Restore In eBPF (CRIB)
+ */
+
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/btf_ids.h>
+
+BTF_KFUNCS_START(bpf_crib_kfuncs)
+
+BTF_ID_FLAGS(func, bpf_iter_task_file_new, KF_ITER_NEW | KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_iter_task_file_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_task_file_get_fd)
+BTF_ID_FLAGS(func, bpf_iter_task_file_destroy, KF_ITER_DESTROY)
+
+BTF_KFUNCS_END(bpf_crib_kfuncs)
+
+static const struct btf_kfunc_id_set bpf_crib_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set   = &bpf_crib_kfuncs,
+};
+
+static int __init bpf_crib_init(void)
+{
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_crib_kfunc_set);
+}
+
+late_initcall(bpf_crib_init);
diff --git a/kernel/bpf/crib/files.c b/kernel/bpf/crib/files.c
new file mode 100644
index 000000000000..ececf150303f
--- /dev/null
+++ b/kernel/bpf/crib/files.c
@@ -0,0 +1,105 @@ 
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/btf.h>
+#include <linux/file.h>
+#include <linux/fdtable.h>
+#include <linux/net.h>
+
+struct bpf_iter_task_file {
+	__u64 __opaque[3];
+} __aligned(8);
+
+struct bpf_iter_task_file_kern {
+	struct task_struct *task;
+	struct file *file;
+	int fd;
+} __aligned(8);
+
+__bpf_kfunc_start_defs();
+
+/**
+ * bpf_iter_task_file_new() - Initialize a new task file iterator for a task,
+ * used to iterate over all files opened by a specified task
+ *
+ * @it: the new bpf_iter_task_file to be created
+ * @task: a pointer pointing to a task to be iterated over
+ */
+__bpf_kfunc int bpf_iter_task_file_new(struct bpf_iter_task_file *it,
+		struct task_struct *task)
+{
+	struct bpf_iter_task_file_kern *kit = (void *)it;
+
+	BUILD_BUG_ON(sizeof(struct bpf_iter_task_file_kern) > sizeof(struct bpf_iter_task_file));
+	BUILD_BUG_ON(__alignof__(struct bpf_iter_task_file_kern) !=
+		     __alignof__(struct bpf_iter_task_file));
+
+	kit->task = task;
+	kit->fd = -1;
+	kit->file = NULL;
+
+	return 0;
+}
+
+/**
+ * bpf_iter_task_file_next() - Get the next file in bpf_iter_task_file
+ *
+ * bpf_iter_task_file_next acquires a reference to the returned struct file.
+ *
+ * The reference to struct file acquired by the previous
+ * bpf_iter_task_file_next() is released in the next bpf_iter_task_file_next(),
+ * and the last reference is released in the last bpf_iter_task_file_next()
+ * that returns NULL.
+ *
+ * @it: the bpf_iter_task_file to be checked
+ *
+ * @returns a pointer to the struct file of the next file if further files
+ * are available, otherwise returns NULL
+ */
+__bpf_kfunc struct file *bpf_iter_task_file_next(struct bpf_iter_task_file *it)
+{
+	struct bpf_iter_task_file_kern *kit = (void *)it;
+
+	if (kit->file)
+		fput(kit->file);
+
+	kit->fd++;
+
+	rcu_read_lock();
+	kit->file = task_lookup_next_fdget_rcu(kit->task, &kit->fd);
+	rcu_read_unlock();
+
+	return kit->file;
+}
+
+/**
+ * bpf_iter_task_file_get_fd() - Get the file descriptor corresponding to
+ * the file in the current iteration
+ *
+ * @it: the bpf_iter_task_file to be checked
+ *
+ * @returns the file descriptor
+ */
+__bpf_kfunc int bpf_iter_task_file_get_fd(struct bpf_iter_task_file *it__iter)
+{
+	struct bpf_iter_task_file_kern *kit = (void *)it__iter;
+
+	return kit->fd;
+}
+
+/**
+ * bpf_iter_task_file_destroy() - Destroy a bpf_iter_task_file
+ *
+ * If the iterator does not iterate to the end, then the last
+ * struct file reference is released at this time.
+ *
+ * @it: the bpf_iter_task_file to be destroyed
+ */
+__bpf_kfunc void bpf_iter_task_file_destroy(struct bpf_iter_task_file *it)
+{
+	struct bpf_iter_task_file_kern *kit = (void *)it;
+
+	if (kit->file)
+		fput(kit->file);
+}
+
+__bpf_kfunc_end_defs();