From: Andrii Nakryiko <andrii@kernel.org>
Date: Tue, 23 Nov 2021 16:23:18 -0800
Subject: libbpf: Fix using invalidated memory in bpf_linker
Patch-mainline: v5.17-rc1
Git-commit: 593835377f24ca1bb98008ec1dc3baefe491ad6e
References: jsc#PED-1368

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@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211124002325.1737739-7-andrii@kernel.org
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 tools/lib/bpf/linker.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- 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(struc
 			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;