[PATCH AUTOSEL 5.2 02/76] libbpf: fix erroneous multi-closing of BTF FD

Sasha Levin
2019-08-29T18:13:24Z

From: Andrii Nakryiko <andriin@fb.com>

[ Upstream commit 5d01ab7bac467edfc530e6ccf953921def935c62 ]

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: 2993e0515bb4 ("tools/bpf: add support to read .BTF.ext sections")
Reported-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/libbpf.c | 11 +++--------
1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3865a5d272514..e308fcf16cdd0 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -178,7 +178,6 @@ 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;
@@ -305,7 +304,6 @@ 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);
}
@@ -382,7 +380,6 @@ 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:
@@ -1883,9 +1880,6 @@ 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;
}

@@ -2060,7 +2054,7 @@ 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;

memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
load_attr.prog_type = prog->type;
@@ -2072,7 +2066,8 @@ 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;
--
2.20.1