[PATCH bpf-next 3/3] bpf: Force cookies array to follow symbols sorting

[Jiri Olsa <jolsa@kernel.org>]

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);
+		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);
+		}
+
 		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