On Tue, May 17, 2022 at 12:36 AM Eugene Syromiatnikov <esyr@xxxxxxxxxx> wrote:
>
> Check that size would not overflow before calculation (and return
> -EOVERFLOW if it will), to prevent potential out-of-bounds write
> with the following copy_from_user. Use kvmalloc_array
> in copy_user_syms to prevent out-of-bounds write into syms
> (and especially buf) as well.
>
> Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.18
> Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
> ---
> kernel/trace/bpf_trace.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 7141ca8..9c041be 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2261,11 +2261,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
> int err = -ENOMEM;
> unsigned int i;
>
> - syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> + syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
> if (!syms)
> goto error;
>
> - buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> + buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
> if (!buf)
> goto error;
>
> @@ -2461,7 +2461,8 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
> if (!cnt)
> return -EINVAL;
>
> - size = cnt * sizeof(*addrs);
> + if (check_mul_overflow(cnt, (u32)sizeof(*addrs), &size))
> + return -EOVERFLOW;
> addrs = kvmalloc(size, GFP_KERNEL);
any good reason not to use kvmalloc_array() here as well and delegate
overflow to it. And then use long size (as expected by copy_from_user
anyway) everywhere?
> if (!addrs)
> return -ENOMEM;
> --
> 2.1.4
>
