[PATCH] bpf: Expose a bpf_sock_from_file helper to tracing programs

[Florent Revest <revest@chromium.org>]

From: Florent Revest <revest@google.com>

eBPF programs can already check whether a file is a socket using
file->f_op == &socket_file_ops but they can not convert file->private_data
into a struct socket with BTF information. For that, we need a new
helper that is essentially just a wrapper for sock_from_file.

sock_from_file can set an err value but this is only set to -ENOTSOCK
when the return value is NULL so it's useless superfluous information.

Signed-off-by: Florent Revest <revest@google.com>
---
 include/uapi/linux/bpf.h       |  7 +++++++
 kernel/trace/bpf_trace.c       | 22 ++++++++++++++++++++++
 scripts/bpf_helpers_doc.py     |  4 ++++
 tools/include/uapi/linux/bpf.h |  7 +++++++
 4 files changed, 40 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 162999b12790..6c96bf9c1f94 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3787,6 +3787,12 @@ union bpf_attr {
  *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.
  *	Return
  *		Pointer to the current task.
+ *
+ * struct socket *bpf_sock_from_file(struct file *file)
+ *	Description
+ *		If the given file contains a socket, returns the associated socket.
+ *	Return
+ *		A pointer to a struct socket on success, or NULL on failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3954,7 @@ union bpf_attr {
 	FN(task_storage_get),		\
 	FN(task_storage_delete),	\
 	FN(get_current_task_btf),	\
+	FN(sock_from_file),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3530120fa280..d040d3ec8313 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1255,6 +1255,26 @@ const struct bpf_func_proto bpf_snprintf_btf_proto = {
 	.arg5_type	= ARG_ANYTHING,
 };
 
+BPF_CALL_1(bpf_sock_from_file, struct file *, file)
+{
+	int err;
+
+	return (unsigned long) sock_from_file(file, &err);
+}
+
+BTF_ID_LIST(bpf_sock_from_file_btf_ids)
+BTF_ID(struct, socket)
+BTF_ID(struct, file)
+
+const struct bpf_func_proto bpf_sock_from_file_proto = {
+	.func		= bpf_sock_from_file,
+	.gpl_only	= true,
+	.ret_type	= RET_PTR_TO_BTF_ID_OR_NULL,
+	.ret_btf_id	= &bpf_sock_from_file_btf_ids[0],
+	.arg1_type	= ARG_PTR_TO_BTF_ID,
+	.arg1_btf_id	= &bpf_sock_from_file_btf_ids[1],
+};
+
 const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -1349,6 +1369,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_per_cpu_ptr_proto;
 	case BPF_FUNC_bpf_this_cpu_ptr:
 		return &bpf_this_cpu_ptr_proto;
+	case BPF_FUNC_sock_from_file:
+		return &bpf_sock_from_file_proto;
 	default:
 		return NULL;
 	}
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index 6769caae142f..99068ec40315 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -434,6 +434,8 @@ class PrinterHelpers(Printer):
             'struct xdp_md',
             'struct path',
             'struct btf_ptr',
+            'struct socket',
+            'struct file',
     ]
     known_types = {
             '...',
@@ -477,6 +479,8 @@ class PrinterHelpers(Printer):
             'struct task_struct',
             'struct path',
             'struct btf_ptr',
+            'struct socket',
+            'struct file',
     }
     mapped_types = {
             'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 162999b12790..6c96bf9c1f94 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3787,6 +3787,12 @@ union bpf_attr {
  *		*ARG_PTR_TO_BTF_ID* of type *task_struct*.
  *	Return
  *		Pointer to the current task.
+ *
+ * struct socket *bpf_sock_from_file(struct file *file)
+ *	Description
+ *		If the given file contains a socket, returns the associated socket.
+ *	Return
+ *		A pointer to a struct socket on success, or NULL on failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3948,6 +3954,7 @@ union bpf_attr {
 	FN(task_storage_get),		\
 	FN(task_storage_delete),	\
 	FN(get_current_task_btf),	\
+	FN(sock_from_file),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.29.2.222.g5d2a92d10f8-goog