On Fri, May 27, 2022 at 1:57 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> When user specifies symbols and cookies for kprobe_multi link
> interface it's very likely the cookies will be misplaced and
> returned to wrong functions (via get_attach_cookie helper).
>
> The reason is that to resolve the provided functions we sort
> them before passing them to ftrace_lookup_symbols, but we do
> not do the same sort on the cookie values.
>
> Fixing this by using sort_r function with custom swap callback
> that swaps cookie values as well.
>
> Fixes: 0236fec57a15 ("bpf: Resolve symbols with ftrace_lookup_symbols for kprobe multi link")
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> kernel/trace/bpf_trace.c | 65 ++++++++++++++++++++++++++++++----------
> 1 file changed, 50 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 10b157a6d73e..e5c423b835ab 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2423,7 +2423,12 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
> kprobe_multi_link_prog_run(link, entry_ip, regs);
> }
>
> -static int symbols_cmp(const void *a, const void *b)
> +struct multi_symbols_sort {
> + const char **funcs;
> + u64 *cookies;
> +};
> +
> +static int symbols_cmp_r(const void *a, const void *b, const void *priv)
> {
> const char **str_a = (const char **) a;
> const char **str_b = (const char **) b;
> @@ -2431,6 +2436,25 @@ static int symbols_cmp(const void *a, const void *b)
> return strcmp(*str_a, *str_b);
> }
>
> +static void symbols_swap_r(void *a, void *b, int size, const void *priv)
> +{
> + const struct multi_symbols_sort *data = priv;
> + const char **name_a = a, **name_b = b;
> + u64 *cookie_a, *cookie_b;
> +
> + cookie_a = data->cookies + (name_a - data->funcs);
> + cookie_b = data->cookies + (name_b - data->funcs);
> +
> + /* swap name_a/name_b and cookie_a/cookie_b values */
> + swap(*name_a, *name_b);
> + swap(*cookie_a, *cookie_b);
> +}
> +
> +static int symbols_cmp(const void *a, const void *b)
> +{
> + return symbols_cmp_r(a, b, NULL);
> +}
> +
> int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> {
> struct bpf_kprobe_multi_link *link = NULL;
> @@ -2468,6 +2492,19 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> if (!addrs)
> return -ENOMEM;
>
> + ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
> + if (ucookies) {
> + cookies = kvmalloc(size, GFP_KERNEL);
> + if (!cookies) {
> + err = -ENOMEM;
> + goto error;
> + }
> + if (copy_from_user(cookies, ucookies, size)) {
> + err = -EFAULT;
> + goto error;
> + }
> + }
> +
> if (uaddrs) {
> if (copy_from_user(addrs, uaddrs, size)) {
> err = -EFAULT;
> @@ -2480,26 +2517,24 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> if (err)
> goto error;
>
> - sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL);
> + if (cookies) {
> + struct multi_symbols_sort data = {
> + .cookies = cookies,
> + .funcs = us.syms,
> + };
> +
> + sort_r(us.syms, cnt, sizeof(*us.syms), symbols_cmp_r,
> + symbols_swap_r, &data);
> + } else {
> + sort(us.syms, cnt, sizeof(*us.syms), symbols_cmp, NULL);
> + }
maybe just always do sort_r, swap callback can just check if cookie
array is NULL and if not, additionally swap cookies? why have all
these different callbacks and complicate the code unnecessarily?
> +
> err = ftrace_lookup_symbols(us.syms, cnt, addrs);
> free_user_syms(&us);
> if (err)
> goto error;
> }
>
> - ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
> - if (ucookies) {
> - cookies = kvmalloc(size, GFP_KERNEL);
> - if (!cookies) {
> - err = -ENOMEM;
> - goto error;
> - }
> - if (copy_from_user(cookies, ucookies, size)) {
> - err = -EFAULT;
> - goto error;
> - }
> - }
> -
> link = kzalloc(sizeof(*link), GFP_KERNEL);
> if (!link) {
> err = -ENOMEM;
> --
> 2.35.3
>
