[PATCH bpf v2] libbpf: don't crash on object files with no symbol tables

[PATCH bpf v2] libbpf: don't crash on object files with no symbol tables

[Toke Høiland-Jørgensen]

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>
---
 tools/lib/bpf/libbpf.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 6f5e2757bb3c..997060182cef 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2990,6 +2990,12 @@ 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++;
-- 
2.33.0

Re: [PATCH bpf v2] libbpf: don't crash on object files with no symbol tables

[Andrii Nakryiko]

On Wed, Sep 1, 2021 at 4:48 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> 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>
> ---

Applied to bpf-next, thanks.


>  tools/lib/bpf/libbpf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 6f5e2757bb3c..997060182cef 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -2990,6 +2990,12 @@ 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++;
> --
> 2.33.0
>