linux-kernel - [PATCH bpf-next] bpf: Replace offsetof() with struct

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Message-ID: <20250503151513.343931-2-thorsten.blum@linux.dev>
Date: Sat,  3 May 2025 17:15:13 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Martin KaFai Lau <martin.lau@...ux.dev>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>
Cc: Thorsten Blum <thorsten.blum@...ux.dev>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next] bpf: Replace offsetof() with struct_size()

Compared to offsetof(), struct_size() provides additional compile-time
checks for structs with flexible arrays (e.g., __must_be_array()).

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
---
 kernel/bpf/btf.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 16ba36f34dfa..58a6092a7ff8 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -26,6 +26,7 @@
 #include <linux/bsearch.h>
 #include <linux/kobject.h>
 #include <linux/sysfs.h>
+#include <linux/overflow.h>
 
 #include <net/netfilter/nf_bpf_link.h>
 
@@ -3957,7 +3958,7 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
 	/* This needs to be kzalloc to zero out padding and unused fields, see
 	 * comment in btf_record_equal.
 	 */
-	rec = kzalloc(offsetof(struct btf_record, fields[cnt]), GFP_KERNEL | __GFP_NOWARN);
+	rec = kzalloc(struct_size(rec, fields, cnt), GFP_KERNEL | __GFP_NOWARN);
 	if (!rec)
 		return ERR_PTR(-ENOMEM);
 
@@ -5583,7 +5584,7 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
 		if (id < 0)
 			continue;
 
-		new_aof = krealloc(aof, offsetof(struct btf_id_set, ids[aof->cnt + 1]),
+		new_aof = krealloc(aof, struct_size(new_aof, ids, aof->cnt + 1),
 				   GFP_KERNEL | __GFP_NOWARN);
 		if (!new_aof) {
 			ret = -ENOMEM;
@@ -5610,7 +5611,7 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
 		if (ret != BTF_FIELD_FOUND)
 			continue;
 
-		new_aof = krealloc(aof, offsetof(struct btf_id_set, ids[aof->cnt + 1]),
+		new_aof = krealloc(aof, struct_size(new_aof, ids, aof->cnt + 1),
 				   GFP_KERNEL | __GFP_NOWARN);
 		if (!new_aof) {
 			ret = -ENOMEM;
@@ -5647,7 +5648,7 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
 		continue;
 	parse:
 		tab_cnt = tab ? tab->cnt : 0;
-		new_tab = krealloc(tab, offsetof(struct btf_struct_metas, types[tab_cnt + 1]),
+		new_tab = krealloc(tab, struct_size(new_tab, types, tab_cnt + 1),
 				   GFP_KERNEL | __GFP_NOWARN);
 		if (!new_tab) {
 			ret = -ENOMEM;
@@ -8563,7 +8564,7 @@ static int btf_populate_kfunc_set(struct btf *btf, enum btf_kfunc_hook hook,
 
 	/* Grow set */
 	set = krealloc(tab->sets[hook],
-		       offsetof(struct btf_id_set8, pairs[set_cnt + add_set->cnt]),
+		       struct_size(set, pairs, set_cnt + add_set->cnt),
 		       GFP_KERNEL | __GFP_NOWARN);
 	if (!set) {
 		ret = -ENOMEM;
@@ -8849,7 +8850,7 @@ int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_c
 	}
 
 	tab = krealloc(btf->dtor_kfunc_tab,
-		       offsetof(struct btf_id_dtor_kfunc_tab, dtors[tab_cnt + add_cnt]),
+		       struct_size(tab, dtors, tab_cnt + add_cnt),
 		       GFP_KERNEL | __GFP_NOWARN);
 	if (!tab) {
 		ret = -ENOMEM;
@@ -9407,8 +9408,7 @@ btf_add_struct_ops(struct btf *btf, struct bpf_struct_ops *st_ops,
 
 	tab = btf->struct_ops_tab;
 	if (!tab) {
-		tab = kzalloc(offsetof(struct btf_struct_ops_tab, ops[4]),
-			      GFP_KERNEL);
+		tab = kzalloc(struct_size(tab, ops, 4), GFP_KERNEL);
 		if (!tab)
 			return -ENOMEM;
 		tab->capacity = 4;
@@ -9421,8 +9421,7 @@ btf_add_struct_ops(struct btf *btf, struct bpf_struct_ops *st_ops,
 
 	if (tab->cnt == tab->capacity) {
 		new_tab = krealloc(tab,
-				   offsetof(struct btf_struct_ops_tab,
-					    ops[tab->capacity * 2]),
+				   struct_size(tab, ops, tab->capacity * 2),
 				   GFP_KERNEL);
 		if (!new_tab)
 			return -ENOMEM;
-- 
2.49.0