[PATCH bpf v1] libbpf: fix accessing BTF.ext core_relo header

[Tony Ambardar <tony.ambardar@gmail.com>]

From: Tony Ambardar <tony.ambardar@gmail.com>

Update btf_ext_parse_info() to ensure the core_relo header is present
before reading its fields. This avoids a potential buffer read overflow
reported by the OSS Fuzz project.

Fixes: cf579164e9ea ("libbpf: Support BTF.ext loading and output in either endianness")
Link: https://issues.oss-fuzz.com/issues/388905046
Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
---
 tools/lib/bpf/btf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 48c66f3a9200..560b519f820e 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -3015,8 +3015,6 @@ static int btf_ext_parse_info(struct btf_ext *btf_ext, bool is_native)
 		.desc = "line_info",
 	};
 	struct btf_ext_sec_info_param core_relo = {
-		.off = btf_ext->hdr->core_relo_off,
-		.len = btf_ext->hdr->core_relo_len,
 		.min_rec_size = sizeof(struct bpf_core_relo),
 		.ext_info = &btf_ext->core_relo_info,
 		.desc = "core_relo",
@@ -3034,6 +3032,8 @@ static int btf_ext_parse_info(struct btf_ext *btf_ext, bool is_native)
 	if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len))
 		return 0; /* skip core relos parsing */
 
+	core_relo.off = btf_ext->hdr->core_relo_off;
+	core_relo.len = btf_ext->hdr->core_relo_len;
 	err = btf_ext_parse_sec_info(btf_ext, &core_relo, is_native);
 	if (err)
 		return err;
-- 
2.34.1