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SubjectRe: [PATCH] bpf, libbpf: Smatch: Fix potential NULL pointer dereference
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On 07/02/2019 12:25 PM, Leo Yan wrote:
> 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.yan@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,
> - };

Applied, thanks! Fyi, I retained the zeroing of open_attr as otherwise if we ever
extend struct bpf_object_open_attr in future, we'll easily miss this and pass in
garbage to bpf_object__open_xattr().

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