On Thu, Mar 10, 2022 at 11:56:20PM +0100, Toke Høiland-Jørgensen wrote:
> The live packet mode uses some extra space at the start of each page to
> cache data structures so they don't have to be rebuilt at every repetition.
> This space wasn't correctly accounted for in the size checking of the
> arguments supplied to userspace. In addition, the definition of the frame
> size should include the size of the skb_shared_info (as there is other
> logic that subtracts the size of this).
>
> Together, these mistakes resulted in userspace being able to trip the
> XDP_WARN() in xdp_update_frame_from_buff(), which syzbot discovered in
> short order. Fix this by changing the frame size define and adding the
> extra headroom to the bpf_prog_test_run_xdp() function. Also drop the
> max_len parameter to the page_pool init, since this is related to DMA which
> is not used for the page pool instance in PROG_TEST_RUN.
>
> Reported-by: syzbot+0e91362d99386dc5de99@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: b530e9e1063e ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN")
> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
> net/bpf/test_run.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 24405a280a9b..e7b9c2636d10 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -112,8 +112,7 @@ struct xdp_test_data {
> u32 frame_cnt;
> };
>
> -#define TEST_XDP_FRAME_SIZE (PAGE_SIZE - sizeof(struct xdp_page_head) \
> - - sizeof(struct skb_shared_info))
> +#define TEST_XDP_FRAME_SIZE (PAGE_SIZE - sizeof(struct xdp_page_head))
> #define TEST_XDP_MAX_BATCH 256
>
> static void xdp_test_run_init_page(struct page *page, void *arg)
> @@ -156,7 +155,6 @@ static int xdp_test_run_setup(struct xdp_test_data *xdp, struct xdp_buff *orig_c
> .flags = 0,
> .pool_size = xdp->batch_size,
> .nid = NUMA_NO_NODE,
> - .max_len = TEST_XDP_FRAME_SIZE,
> .init_callback = xdp_test_run_init_page,
> .init_arg = xdp,
> };
> @@ -1230,6 +1228,8 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
> batch_size = NAPI_POLL_WEIGHT;
> else if (batch_size > TEST_XDP_MAX_BATCH)
> return -E2BIG;
> +
> + headroom += sizeof(struct xdp_page_head);
The orig_ctx->data_end will ensure there is a sizeof(struct skb_shared_info)
tailroom ? It is quite tricky to read but I don't have a better idea
either.
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
> } else if (batch_size) {
> return -EINVAL;
> }
> --
> 2.35.1
>
