linux-kernel - [PATCH 5.16 0173/1039] libbpf: Fix using invalidated memory in bpf

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Date:   Mon, 24 Jan 2022 19:32:42 +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>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 0173/1039] libbpf: Fix using invalidated memory in bpf_linker

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

[ Upstream commit 593835377f24ca1bb98008ec1dc3baefe491ad6e ]

add_dst_sec() can invalidate bpf_linker's section index making
dst_symtab pointer pointing into unallocated memory. Reinitialize
dst_symtab pointer on each iteration to make sure it's always valid.

Fixes: faf6ed321cf6 ("libbpf: Add BPF static linker APIs")
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Link: https://lore.kernel.org/bpf/20211124002325.1737739-7-andrii@kernel.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/lib/bpf/linker.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 94bdd97859285..6923a0ab3b127 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -2000,7 +2000,7 @@ add_sym:
 static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *obj)
 {
 	struct src_sec *src_symtab = &obj->secs[obj->symtab_sec_idx];
-	struct dst_sec *dst_symtab = &linker->secs[linker->symtab_sec_idx];
+	struct dst_sec *dst_symtab;
 	int i, err;
 
 	for (i = 1; i < obj->sec_cnt; i++) {
@@ -2033,6 +2033,9 @@ static int linker_append_elf_relos(struct bpf_linker *linker, struct src_obj *ob
 			return -1;
 		}
 
+		/* add_dst_sec() above could have invalidated linker->secs */
+		dst_symtab = &linker->secs[linker->symtab_sec_idx];
+
 		/* shdr->sh_link points to SYMTAB */
 		dst_sec->shdr->sh_link = linker->symtab_sec_idx;
 
-- 
2.34.1