linux-kernel - [PATCH 5.16 0107/1039] libbpf: Fix section counting logic

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Date:   Mon, 24 Jan 2022 19:31:36 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 0107/1039] libbpf: Fix section counting logic

From: Andrii Nakryiko <andrii@...nel.org>

[ Upstream commit 0d6988e16a12ebd41d3e268992211b0ceba44ed7 ]

e_shnum does include section #0 and as such is exactly the number of ELF
sections that we need to allocate memory for to use section indices as
array indices. Fix the off-by-one error.

This is purely accounting fix, previously we were overallocating one
too many array items. But no correctness errors otherwise.

Fixes: 25bbbd7a444b ("libbpf: Remove assumptions about uniqueness of .rodata/.data/.bss maps")
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Yonghong Song <yhs@...com>
Link: https://lore.kernel.org/bpf/20211103173213.1376990-5-andrii@kernel.org
Signed-off-by: Sasha Levin <sashal@...nel.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 7c74342bb6680..5367bc8e52073 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -3191,11 +3191,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 	Elf_Scn *scn;
 	Elf64_Shdr *sh;
 
-	/* ELF section indices are 1-based, so allocate +1 element to keep
-	 * indexing simple. Also include 0th invalid section into sec_cnt for
-	 * simpler and more traditional iteration logic.
+	/* ELF section indices are 0-based, but sec #0 is special "invalid"
+	 * section. e_shnum does include sec #0, so e_shnum is the necessary
+	 * size of an array to keep all the sections.
 	 */
-	obj->efile.sec_cnt = 1 + obj->efile.ehdr->e_shnum;
+	obj->efile.sec_cnt = obj->efile.ehdr->e_shnum;
 	obj->efile.secs = calloc(obj->efile.sec_cnt, sizeof(*obj->efile.secs));
 	if (!obj->efile.secs)
 		return -ENOMEM;
-- 
2.34.1