From 9fad7fe5b29803584c7f17a2abe6c2936fec6828 Mon Sep 17 00:00:00 2001
From: Jules Irenge <jbi.octave@gmail.com>
Date: Wed, 7 Sep 2022 16:24:20 +0100
Subject: [PATCH] bpf: Fix resetting logic for unreferenced kptrs
Sparse reported a warning at bpf_map_free_kptrs()
"warning: Using plain integer as NULL pointer"
During the process of fixing this warning, it was discovered that the current
code erroneously writes to the pointer variable instead of deferencing and
writing to the actual kptr. Hence, Sparse tool accidentally helped to uncover
this problem. Fix this by doing WRITE_ONCE(*p, 0) instead of WRITE_ONCE(p, 0).
Note that the effect of this bug is that unreferenced kptrs will not be cleared
during check_and_free_fields. It is not a problem if the clearing is not done
during map_free stage, as there is nothing to free for them.
Fixes: 14a324f6a67e ("bpf: Wire up freeing of referenced kptr")
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Link: https://lore.kernel.org/r/Yxi3pJaK6UDjVJSy@playground
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
kernel/bpf/syscall.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 4fb08c43420d1..d35a6aa3aa963 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -598,7 +598,7 @@ void bpf_map_free_kptrs(struct bpf_map *map, void *map_value)
if (off_desc->type == BPF_KPTR_UNREF) {
u64 *p = (u64 *)btf_id_ptr;
- WRITE_ONCE(p, 0);
+ WRITE_ONCE(*p, 0);
continue;
}
old_ptr = xchg(btf_id_ptr, 0);
--
GitLab