From: Andrii Nakryiko <andriin@fb.com>
Date: Wed, 29 Jul 2020 16:21:48 -0700
Subject: libbpf: Make destructors more robust by handling ERR_PTR(err) cases
Patch-mainline: v5.9-rc1
Git-commit: 50450fc716c1a570ee8d8bfe198ef5d3cfca36e4
References: bsc#1177028

Most of libbpf "constructors" on failure return ERR_PTR(err) result encoded as
a pointer. It's a common mistake to eventually pass such malformed pointers
into xxx__destroy()/xxx__free() "destructors". So instead of fixing up
clean up code in selftests and user programs, handle such error pointers in
destructors themselves. This works beautifully for NULL pointers passed to
destructors, so might as well just work for error pointers.

Suggested-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20200729232148.896125-1-andriin@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
 tools/lib/bpf/btf.c      |    4 ++--
 tools/lib/bpf/btf_dump.c |    2 +-
 tools/lib/bpf/libbpf.c   |    9 ++++-----
 3 files changed, 7 insertions(+), 8 deletions(-)

--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -386,7 +386,7 @@ __s32 btf__find_by_name_kind(const struc
 
 void btf__free(struct btf *btf)
 {
-	if (!btf)
+	if (IS_ERR_OR_NULL(btf))
 		return;
 
 	if (btf->fd >= 0)
@@ -1025,7 +1025,7 @@ static int btf_ext_parse_hdr(__u8 *data,
 
 void btf_ext__free(struct btf_ext *btf_ext)
 {
-	if (!btf_ext)
+	if (IS_ERR_OR_NULL(btf_ext))
 		return;
 	free(btf_ext->data);
 	free(btf_ext);
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -183,7 +183,7 @@ void btf_dump__free(struct btf_dump *d)
 {
 	int i, cnt;
 
-	if (!d)
+	if (IS_ERR_OR_NULL(d))
 		return;
 
 	free(d->type_states);
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6506,7 +6506,7 @@ void bpf_object__close(struct bpf_object
 {
 	size_t i;
 
-	if (!obj)
+	if (IS_ERR_OR_NULL(obj))
 		return;
 
 	if (obj->clear_priv)
@@ -7692,7 +7692,7 @@ int bpf_link__destroy(struct bpf_link *l
 {
 	int err = 0;
 
-	if (!link)
+	if (IS_ERR_OR_NULL(link))
 		return 0;
 
 	if (!link->disconnected && link->detach)
@@ -8505,7 +8505,7 @@ void perf_buffer__free(struct perf_buffe
 {
 	int i;
 
-	if (!pb)
+	if (IS_ERR_OR_NULL(pb))
 		return;
 	if (pb->cpu_bufs) {
 		for (i = 0; i < pb->cpu_cnt; i++) {
@@ -9382,8 +9382,7 @@ void bpf_object__detach_skeleton(struct
 	for (i = 0; i < s->prog_cnt; i++) {
 		struct bpf_link **link = s->progs[i].link;
 
-		if (!IS_ERR_OR_NULL(*link))
-			bpf_link__destroy(*link);
+		bpf_link__destroy(*link);
 		*link = NULL;
 	}
 }