libbpf: Don't crash on object files with no symbol tables

[ Upstream commit 03e601f48b2da6fb44d0f7b86957a8f6bacfb347 ]

If libbpf encounters an ELF file that has been stripped of its symbol
table, it will crash in bpf_object__add_programs() when trying to
dereference the obj->efile.symbols pointer.

Fix this by erroring out of bpf_object__elf_collect() if it is not able
able to find the symbol table.

v2:
  - Move check into bpf_object__elf_collect() and add nice error message

Fixes: 6245947c1b3c ("libbpf: Allow gaps in BPF program sections to support overriden weak functions")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210901114812.204720-1-toke@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e4f83c3..51180f3 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2993,6 +2993,12 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                }
        }
 
+       if (!obj->efile.symbols) {
+               pr_warn("elf: couldn't find symbol table in %s, stripped object file?\n",
+                       obj->path);
+               return -ENOENT;
+       }
+
        scn = NULL;
        while ((scn = elf_nextscn(elf, scn)) != NULL) {
                idx++;