On Thu, Jun 02, 2022 at 04:02:28PM -0700, Andrii Nakryiko wrote:

On Thu, Jun 2, 2022 at 4:01 PM Andrii Nakryiko
[off-list ref] wrote:

quoted

On Fri, May 27, 2022 at 1:57 PM Jiri Olsa [off-list ref] wrote:

quoted

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@kernel.org>
---
 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);

oh, and you'll have to rebase anyways after kvmalloc_array patch

true, that kvmalloc_array change went to bpf-next/master,
but as Song mentioned this patchset should probably go for bpf/master?

I'm fine either way, let me know ;-)

thanks,
jirka