Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [Medium] libbpf: type confusion between iter_info and log_opts in bpf_link_create() --
commit b4af2771f4c0edb6656b6ddcd881019158c55a55 Author: Leon Hwang <[email protected]> libbpf: Add log_opts support for bpf_link_create This commit adds log_opts support to bpf_link_create() by placing log_opts in an anonymous union with iter_info in struct bpf_link_create_opts and passing it to __sys_bpf_fd(). > diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c > index aea534764dfe2..38dcb31e8c0ed 100644 > --- a/tools/lib/bpf/bpf.c > +++ b/tools/lib/bpf/bpf.c > @@ -794,6 +794,8 @@ int bpf_link_create(int prog_fd, int target_fd, > { > const size_t attr_sz = offsetofend(union bpf_attr, link_create); > __u32 target_btf_id, iter_info_len, relative_id; > + union bpf_iter_link_info *iter_info = NULL; > + struct bpf_log_opts *log_opts = NULL; > int fd, err, relative_fd; > union bpf_attr attr; > > @@ -803,6 +805,14 @@ int bpf_link_create(int prog_fd, int target_fd, > iter_info_len = OPTS_GET(opts, iter_info_len, 0); > target_btf_id = OPTS_GET(opts, target_btf_id, 0); > > + if (iter_info_len && attach_type != BPF_TRACE_ITER) > + return libbpf_err(-EINVAL); > + > + if (iter_info_len) > + iter_info = OPTS_GET(opts, iter_info, (void *)0); > + else > + log_opts = OPTS_GET(opts, log_opts, (void *)0); [Severity: Medium] Can overlaying iter_info and log_opts in struct bpf_link_create_opts and selecting between them using only iter_info_len cause type confusion when a caller passes a non-NULL iter_info with iter_info_len == 0? For example, a caller of bpf_link_create() or bpf_program__attach_iter() in tools/lib/bpf/libbpf.c: tools/lib/bpf/libbpf.c:bpf_program__attach_iter() { ... link_create_opts.iter_info = OPTS_GET(opts, link_info, (void *)0); link_create_opts.iter_info_len = OPTS_GET(opts, link_info_len, 0); ... return bpf_link_create(prog_fd, target_fd, BPF_TRACE_ITER, &link_create_opts); } might pass a non-NULL union bpf_iter_link_info pointer while leaving iter_info_len (or link_info_len) set to 0. Previously, bpf_link_create() forwarded both the non-NULL iter_info pointer and iter_info_len == 0 to the kernel, where bpf_iter_link_attach() rejected the mismatched arguments with -EINVAL: kernel/bpf/bpf_iter.c:bpf_iter_link_attach() { ... if (bpfptr_is_null(ulinfo) ^ !linfo_len) return -EINVAL; ... } With this change, when iter_info_len == 0, bpf_link_create() leaves iter_info as NULL (so attr.link_create.iter_info is 0 and the kernel check is bypassed) and instead assigns the union bpf_iter_link_info pointer to log_opts. When bpf_link_create() then calls __sys_bpf_fd(), log_opts is dereferenced as struct bpf_log_opts: tools/lib/bpf/bpf.c:__sys_bpf_fd() { ... if (!OPTS_VALID(log_opts, bpf_log_opts)) return libbpf_err(-EINVAL); if (log_opts && feat_supported(NULL, FEAT_BPF_SYSCALL_COMMON_ATTRS)) { memset(&attr_common, 0, attr_common_sz); attr_common.log_buf = ptr_to_u64(OPTS_GET(log_opts, buf, NULL)); attr_common.log_size = OPTS_GET(log_opts, size, 0); attr_common.log_level = OPTS_GET(log_opts, level, 0); fd = sys_bpf_ext_fd(cmd, attr, attr_sz, &attr_common, attr_common_sz); OPTS_SET(log_opts, true_size, attr_common.log_true_size); } else { fd = sys_bpf_fd(cmd, attr, attr_sz); OPTS_SET(log_opts, true_size, 0); } ... } Since union bpf_iter_link_info is 16 bytes while struct bpf_log_opts extends to offsetofend(struct bpf_log_opts, true_size) (28 bytes on 64-bit, 20 bytes on 32-bit), interpreting the first sizeof(size_t) bytes of iter_info (such as map.map_fd, task.tid, task.pid, or cgroup.cgroup_fd) as log_opts->sz can cause out-of-bounds reads in OPTS_VALID() and OPTS_GET(), as well as a 4-byte out-of-bounds write past union bpf_iter_link_info via OPTS_SET(log_opts, true_size, ...). In addition, aliasing iter_info and log_opts prevents BPF_TRACE_ITER links from using log_opts whenever iter_info is specified. Would it be safer to place log_opts in its own field at the end of struct bpf_link_create_opts instead of sharing a union with iter_info? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=5
