From 4ab07209d5cc8cb6d2a5324c07b3efc3b2fde494 Mon Sep 17 00:00:00 2001 From: Dave Marchevsky Date: Fri, 21 Apr 2023 00:44:31 -0700 Subject: 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 Reported-by: Eduard Zingerman Signed-off-by: Dave Marchevsky Signed-off-by: Daniel Borkmann Tested-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20230421074431.3548349-1-davemarchevsky@fb.com --- kernel/bpf/helpers.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/bpf') diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 00e5fb0682ac..8d368fa353f9 100644 --- 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; -- cgit v1.2.3