From a3debf177f21c687b87b03ca4c193d2a78144804 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 24 Sep 2021 08:07:25 +0530 Subject: [PATCH] libbpf: Fix segfault in static linker for objects without BTF When a BPF object is compiled without BTF info (without -g), trying to link such objects using bpftool causes a SIGSEGV due to btf__get_nr_types accessing obj->btf which is NULL. Fix this by checking for the NULL pointer, and return error. Reproducer: $ cat a.bpf.c extern int foo(void); int bar(void) { return foo(); } $ cat b.bpf.c int foo(void) { return 0; } $ clang -O2 -target bpf -c a.bpf.c $ clang -O2 -target bpf -c b.bpf.c $ bpftool gen obj out a.bpf.o b.bpf.o Segmentation fault (core dumped) After fix: $ bpftool gen obj out a.bpf.o b.bpf.o libbpf: failed to find BTF info for object 'a.bpf.o' Error: failed to link 'a.bpf.o': Unknown error -22 (-22) Fixes: a46349227cd8 (libbpf: Add linker extern resolution support for functions and global variables) Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20210924023725.70228-1-memxor@gmail.com --- tools/lib/bpf/linker.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c index 10911a8cad0f2..2df880cefdaee 100644 --- a/tools/lib/bpf/linker.c +++ b/tools/lib/bpf/linker.c @@ -1649,11 +1649,17 @@ static bool btf_is_non_static(const struct btf_type *t) static int find_glob_sym_btf(struct src_obj *obj, Elf64_Sym *sym, const char *sym_name, int *out_btf_sec_id, int *out_btf_id) { - int i, j, n = btf__get_nr_types(obj->btf), m, btf_id = 0; + int i, j, n, m, btf_id = 0; const struct btf_type *t; const struct btf_var_secinfo *vi; const char *name; + if (!obj->btf) { + pr_warn("failed to find BTF info for object '%s'\n", obj->filename); + return -EINVAL; + } + + n = btf__get_nr_types(obj->btf); for (i = 1; i <= n; i++) { t = btf__type_by_id(obj->btf, i);