[PATCH] bpf, libbpf: Smatch: Fix potential NULL pointer dereference

[Leo Yan]

Based on the following report from Smatch, fix the potential
NULL pointer dereference check.

  tools/lib/bpf/libbpf.c:3493
  bpf_prog_load_xattr() warn: variable dereferenced before check 'attr'
  (see line 3483)

3479 int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
3480                         struct bpf_object **pobj, int *prog_fd)
3481 {
3482         struct bpf_object_open_attr open_attr = {
3483                 .file           = attr->file,
3484                 .prog_type      = attr->prog_type,
                                       ^^^^^^
3485         };

At the head of function, it directly access 'attr' without checking if
it's NULL pointer.  This patch moves the values assignment after
validating 'attr' and 'attr->file'.

Signed-off-by: Leo Yan <leo....@linaro.org>
---
 tools/lib/bpf/libbpf.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 197b574406b3..809b633fa3d9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3479,10 +3479,7 @@ int bpf_prog_load(const char *file, enum bpf_prog_type 
type,
 int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
                        struct bpf_object **pobj, int *prog_fd)
 {
-       struct bpf_object_open_attr open_attr = {
-               .file           = attr->file,
-               .prog_type      = attr->prog_type,
-       };
+       struct bpf_object_open_attr open_attr;
        struct bpf_program *prog, *first_prog = NULL;
        enum bpf_attach_type expected_attach_type;
        enum bpf_prog_type prog_type;
@@ -3495,6 +3492,9 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr 
*attr,
        if (!attr->file)
                return -EINVAL;
 
+       open_attr.file = attr->file;
+       open_attr.prog_type = attr->prog_type;
+
        obj = bpf_object__open_xattr(&open_attr);
        if (IS_ERR_OR_NULL(obj))
                return -ENOENT;
-- 
2.17.1