From: Alexei Starovoitov <ast@xxxxxxxxxx>
Add bpf_sys_close() helper to be used by the syscall/loader program to close
intermediate FDs and other cleanup.
Note this helper must never be allowed inside fdget/fdput bracketing.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
include/uapi/linux/bpf.h | 7 +++++++
kernel/bpf/syscall.c | 19 +++++++++++++++++++
tools/include/uapi/linux/bpf.h | 7 +++++++
3 files changed, 33 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 3cc07351c1cf..4cd9a0181f27 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4754,6 +4754,12 @@ union bpf_attr {
* Find BTF type with given name and kind in vmlinux BTF or in module's BTFs.
* Return
* Returns btf_id and btf_obj_fd in lower and upper 32 bits.
+ *
+ * long bpf_sys_close(u32 fd)
+ * Description
+ * Execute close syscall for given FD.
+ * Return
+ * A syscall result.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -4924,6 +4930,7 @@ union bpf_attr {
FN(snprintf), \
FN(sys_bpf), \
FN(btf_find_by_name_kind), \
+ FN(sys_close), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index f93ff2ebf96d..0f1ce2171f1e 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4578,6 +4578,23 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return bpf_base_func_proto(func_id);
}
+BPF_CALL_1(bpf_sys_close, u32, fd)
+{
+ /* When bpf program calls this helper there should not be
+ * an fdget() without matching completed fdput().
+ * This helper is allowed in the following callchain only:
+ * sys_bpf->prog_test_run->bpf_prog->bpf_sys_close
+ */
+ return close_fd(fd);
+}
+
+const struct bpf_func_proto bpf_sys_close_proto = {
+ .func = bpf_sys_close,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_ANYTHING,
+};
+
static const struct bpf_func_proto *
syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
{
@@ -4586,6 +4603,8 @@ syscall_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_sys_bpf_proto;
case BPF_FUNC_btf_find_by_name_kind:
return &bpf_btf_find_by_name_kind_proto;
+ case BPF_FUNC_sys_close:
+ return &bpf_sys_close_proto;
default:
return tracing_prog_func_proto(func_id, prog);
}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 3cc07351c1cf..4cd9a0181f27 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4754,6 +4754,12 @@ union bpf_attr {
* Find BTF type with given name and kind in vmlinux BTF or in module's BTFs.
* Return
* Returns btf_id and btf_obj_fd in lower and upper 32 bits.
+ *
+ * long bpf_sys_close(u32 fd)
+ * Description
+ * Execute close syscall for given FD.
+ * Return
+ * A syscall result.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -4924,6 +4930,7 @@ union bpf_attr {
FN(snprintf), \
FN(sys_bpf), \
FN(btf_find_by_name_kind), \
+ FN(sys_close), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.30.2
