I don't understand why we don't check path for NULL, bpf_link__pin is an external interface, It will be called by external functions and provide input parameters, for example in samples/bpf/hbm.c:
201 link = bpf_program__attach_cgroup(bpf_prog, cg1); 202 if (libbpf_get_error(link)) { 203 fprintf(stderr, "ERROR: bpf_program__attach_cgroup failed\n"); 204 goto err; 205 } 206 207 sprintf(cg_pin_path, "/sys/fs/bpf/hbm%d", cg_id); 208 rc = bpf_link__pin(link, cg_pin_path); 209 if (rc < 0) { 210 printf("ERROR: bpf_link__pin failed: %d\n", rc); 211 goto err; 212 }
if cg_pin_path is NULL, strdup(NULL) will trigger a segmentation fault in make_parent_dir, I think we should avoid this and add null-pointer checking for path, just like check_path:
7673 static int check_path(const char *path) 7674 { 7675 char *cp, errmsg[STRERR_BUFSIZE]; 7676 struct statfs st_fs; 7677 char *dname, *dir; 7678 int err = 0; 7679 7680 if (path == NULL) 7681 return -EINVAL; 7682 7683 dname = strdup(path); 7684 if (dname == NULL) 7685 return -ENOMEM; 7686 7687 dir = dirname(dname); 7688 if (statfs(dir, &st_fs)) { 7689 cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg)); 7690 pr_warn("failed to statfs %s: %s\n", dir, cp); 7691 err = -errno; 7692 } 7693 free(dname); 7694 7695 if (!err && st_fs.f_type != BPF_FS_MAGIC) { 7696 pr_warn("specified path %s is not on BPF FS\n", path); 7697 err = -EINVAL; 7698 } 7699 7700 return err; 7701 }
Thanks. 在 2022/4/22 0:55, Andrii Nakryiko 写道:
On Thu, Apr 21, 2022 at 6:01 AM Gaosheng Cui <cuigaosheng1@xxxxxxxxxx> wrote:The make_parent_dir is called without null-pointer checking for path, such as bpf_link__pin. To ensure there is no null-pointer dereference in make_parent_dir, so make_parent_dir requires additional null-pointer checking for path. Signed-off-by: Gaosheng Cui <cuigaosheng1@xxxxxxxxxx> --- tools/lib/bpf/libbpf.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index b53e51884f9e..5786e6184bf5 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -7634,6 +7634,9 @@ static int make_parent_dir(const char *path) char *dname, *dir; int err = 0; + if (path == NULL) + return -EINVAL; +API contract is that path shouldn't be NULL. Just like we don't check link, obj, prog for NULL in every single API, I don't think we need to do it here, unless I'm missing something?dname = strdup(path); if (dname == NULL) return -ENOMEM; -- 2.25.1.
