On Mon, Oct 21, 2024 at 9:28 AM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
>
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> Check the validity of nr_words in bpf_iter_bits_new(). Without this
> check, when multiplication overflow occurs for nr_bits (e.g., when
> nr_words = 0x0400-0001, nr_bits becomes 64), stack corruption may occur
> due to bpf_probe_read_kernel_common(..., nr_bytes = 0x2000-0008).
>
> Fix it by limiting the max value of nr_words to 512.
>
> Fixes: 4665415975b0 ("bpf: Add bits iterator")
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
> ---
> kernel/bpf/helpers.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 62349e206a29..c147f75e1b48 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2851,6 +2851,8 @@ struct bpf_iter_bits {
> __u64 __opaque[2];
> } __aligned(8);
>
> +#define BITS_ITER_NR_WORDS_MAX 512
> +
> struct bpf_iter_bits_kern {
> union {
> unsigned long *bits;
> @@ -2892,6 +2894,8 @@ bpf_iter_bits_new(struct bpf_iter_bits *it, const u64 *unsafe_ptr__ign, u32 nr_w
>
> if (!unsafe_ptr__ign || !nr_words)
> return -EINVAL;
> + if (nr_words > BITS_ITER_NR_WORDS_MAX)
> + return -E2BIG;
It is documented that nr_words cannot exceed 512, not due to overflow
concerns, but because of memory allocation limits. It might be better
to use 512 directly instead of BITS_ITER_NR_WORDS_MAX. Alternatively,
if we decide to keep using the macro, the documentation should be
updated accordingly.
>
> /* Optimization for u64 mask */
> if (nr_bits == 64) {
> --
> 2.29.2
>
--
Regards
Yafang
