bpf: Fix bpf_refcount_acquire's refcount_t address calculation

When calculating the address of the refcount_t struct within a local
kptr, bpf_refcount_acquire_impl should add refcount_off bytes to the
address of the local kptr. Due to some missing parens, the function is
incorrectly adding sizeof(refcount_t) * refcount_off bytes. This patch
fixes the calculation.

Due to the incorrect calculation, bpf_refcount_acquire_impl was trying
to refcount_inc some memory well past the end of local kptrs, resulting
in kasan and refcount complaints, as reported in [0]. In that thread,
Florian and Eduard discovered that bpf selftests written in the new
style - with __success and an expected __retval, specifically - were
not actually being run. As a result, selftests added in bpf_refcount
series weren't really exercising this behavior, and thus didn't unearth
the bug.

With this fixed behavior it's safe to revert commit 7c4b96c0
("selftests/bpf: disable program test run for progs/refcounted_kptr.c"),
this patch does so.

  [0] https://lore.kernel.org/bpf/ZEEp+j22imoN6rn9@strlen.de/

Fixes: 7c50b1cb ("bpf: Add bpf_refcount_acquire kfunc")
Reported-by: Florian Westphal <fw@strlen.de>
Reported-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20230421074431.3548349-1-davemarchevsky@fb.com

kernel/bpf/helpers.c

@@ -1925,7 +1925,7 @@ __bpf_kfunc void *bpf_refcount_acquire_impl(void *p__refcounted_kptr, void *meta
 	/* Could just cast directly to refcount_t *, but need some code using
 	 * bpf_refcount type so that it is emitted in vmlinux BTF
 	 */
-	ref = (struct bpf_refcount *)p__refcounted_kptr + meta->record->refcount_off;
+	ref = (struct bpf_refcount *)(p__refcounted_kptr + meta->record->refcount_off);
 
 	refcount_inc((refcount_t *)ref);
 	return (void *)p__refcounted_kptr;

tools/testing/selftests/bpf/progs/refcounted_kptr.c

@@ -219,7 +219,7 @@ static long __read_from_unstash(int idx)
 #define INSERT_READ_BOTH(rem_tree, rem_list, desc)			\
 SEC("tc")								\
 __description(desc)							\
-__success /* __retval(579) temporarily disabled */			\
+__success __retval(579)							\
 long insert_and_remove_tree_##rem_tree##_list_##rem_list(void *ctx)	\
 {									\
 	long err, tree_data, list_data;					\
@@ -258,7 +258,7 @@ INSERT_READ_BOTH(false, true, "insert_read_both: remove from list");
 #define INSERT_READ_BOTH(rem_tree, rem_list, desc)			\
 SEC("tc")								\
 __description(desc)							\
-__success /* __retval(579) temporarily disabled */			\
+__success __retval(579)							\
 long insert_and_remove_lf_tree_##rem_tree##_list_##rem_list(void *ctx)	\
 {									\
 	long err, tree_data, list_data;					\
@@ -296,7 +296,7 @@ INSERT_READ_BOTH(false, true, "insert_read_both_list_first: remove from list");
 #define INSERT_DOUBLE_READ_AND_DEL(read_fn, read_root, desc)		\
 SEC("tc")								\
 __description(desc)							\
-__success /* temporarily __retval(-1) disabled */			\
+__success __retval(-1)							\
 long insert_double_##read_fn##_and_del_##read_root(void *ctx)		\
 {									\
 	long err, list_data;						\
@@ -329,7 +329,7 @@ INSERT_DOUBLE_READ_AND_DEL(__read_from_list, head, "insert_double_del: 2x read-a
 #define INSERT_STASH_READ(rem_tree, desc)				\
 SEC("tc")								\
 __description(desc)							\
-__success /* __retval(84) temporarily disabled */			\
+__success __retval(84)							\
 long insert_rbtree_and_stash__del_tree_##rem_tree(void *ctx)		\
 {									\
 	long err, tree_data, map_data;					\