On Mon, Jun 29, 2020 at 9:47 PM Alexei Starovoitov
[off-list ref] wrote:

On Mon, Jun 29, 2020 at 3:19 PM Andrii Nakryiko [off-list ref] wrote:

quoted

BPF ringbuf assumes the size to be a multiple of page size and the power of
2 value. The latter is important to avoid division while calculating position
inside the ring buffer and using (N-1) mask instead. This patch fixes omission
to enforce power-of-2 size rule.

Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it")
Signed-off-by: Andrii Nakryiko <redacted>
---
 kernel/bpf/ringbuf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index 180414bb0d3e..dcc8e8b9df10 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c

@@ -132,7 +132,7 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
 {
        struct bpf_ringbuf *rb;

-       if (!data_sz || !PAGE_ALIGNED(data_sz))
+       if (!is_power_of_2(data_sz) || !PAGE_ALIGNED(data_sz))
                return ERR_PTR(-EINVAL);

What's the point checking the same value in two different places?
The check below did that already.

I was initially treating bpf_ringbuf_alloc() as a sort of internal API
that some other code (outside of BPF map) might want to use. But I'll
drop for now, it can always be added later.

quoted

 #ifdef CONFIG_64BIT

@@ -166,7 +166,8 @@ static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
                return ERR_PTR(-EINVAL);

        if (attr->key_size || attr->value_size ||
-           attr->max_entries == 0 || !PAGE_ALIGNED(attr->max_entries))
+           !is_power_of_2(attr->max_entries) ||
+           !PAGE_ALIGNED(attr->max_entries))
                return ERR_PTR(-EINVAL);

        rb_map = kzalloc(sizeof(*rb_map), GFP_USER);
--

2.24.1