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 7c4b96c00043
("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: 7c50b1cb76ac ("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

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 00e5fb0682acc02c03f17e6434449b846ec53bd3..8d368fa353f996a1c3e24714f5c5c8cfe4f4d1c6 100644 (file)
--- a/kernel/bpf/helpers.c
+++ b/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;

diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index b6b2d4f97b19df0efa478c972fc92fcbba2727be..1d348a225140dd50f92c415c0ee113178eb38bd0 100644 (file)
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
+++ b/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;                                  \