Commit 5d01ab7b authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: fix erroneous multi-closing of BTF FD 



Libbpf stores associated BTF FD per each instance of bpf_program. When
program is unloaded, that FD is closed. This is wrong, because leads to
a race and possibly closing of unrelated files, if application
simultaneously opens new files while bpf_programs are unloaded.

It's also unnecessary, because struct btf "owns" that FD, and
btf__free(), called from bpf_object__close() will close it. Thus the fix
is to never have per-program BTF FD and fetch it from obj->btf, when
necessary.

Fixes: 2993e051 ("tools/bpf: add support to read .BTF.ext sections")
Reported-by: default avatarAndrey Ignatov <rdna@fb.com>
Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 0a062ba7

tools/lib/bpf/libbpf.c

+3 −8
Original line number Diff line number Diff line
@@ -182,7 +182,6 @@ struct bpf_program { 
	bpf_program_clear_priv_t clear_priv;



	enum bpf_attach_type expected_attach_type;

	int btf_fd;

	void *func_info;

	__u32 func_info_rec_size;

	__u32 func_info_cnt;
@@ -313,7 +312,6 @@ void bpf_program__unload(struct bpf_program *prog) 
	prog->instances.nr = -1;

	zfree(&prog->instances.fds);



	zclose(prog->btf_fd);

	zfree(&prog->func_info);

	zfree(&prog->line_info);

}
@@ -392,7 +390,6 @@ bpf_program__init(void *data, size_t size, char *section_name, int idx, 
	prog->instances.fds = NULL;

	prog->instances.nr = -1;

	prog->type = BPF_PROG_TYPE_UNSPEC;

	prog->btf_fd = -1;



	return 0;

errout:
@@ -2288,9 +2285,6 @@ bpf_program_reloc_btf_ext(struct bpf_program *prog, struct bpf_object *obj, 
		prog->line_info_rec_size = btf_ext__line_info_rec_size(obj->btf_ext);

	}



	if (!insn_offset)

		prog->btf_fd = btf__fd(obj->btf);



	return 0;

}
@@ -2463,7 +2457,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt, 
	char *cp, errmsg[STRERR_BUFSIZE];

	int log_buf_size = BPF_LOG_BUF_SIZE;

	char *log_buf;

	int ret;

	int btf_fd, ret;



	if (!insns || !insns_cnt)

		return -EINVAL;
@@ -2478,7 +2472,8 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt, 
	load_attr.license = license;

	load_attr.kern_version = kern_version;

	load_attr.prog_ifindex = prog->prog_ifindex;

	load_attr.prog_btf_fd = prog->btf_fd >= 0 ? prog->btf_fd : 0;

	btf_fd = bpf_object__btf_fd(prog->obj);

	load_attr.prog_btf_fd = btf_fd >= 0 ? btf_fd : 0;

	load_attr.func_info = prog->func_info;

	load_attr.func_info_rec_size = prog->func_info_rec_size;

	load_attr.func_info_cnt = prog->func_info_cnt;

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