On Mon, Jan 11, 2021 at 2:32 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> On Mon, Jan 11, 2021 at 11:47:38AM -0800, Stanislav Fomichev wrote:
> > optlen == 0 indicates that the kernel should ignore BPF buffer
> > and use the original one from the user. We, however, forget
> > to free the temporary buffer that we've allocated for BPF.
> >
> > Reported-by: Martin KaFai Lau <kafai@xxxxxx>
> > Fixes: d8fe449a9c51 ("bpf: Don't return EINVAL from {get,set}sockopt when optlen > PAGE_SIZE")
> > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > ---
> > kernel/bpf/cgroup.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> > index 6ec088a96302..09179ab72c03 100644
> > --- a/kernel/bpf/cgroup.c
> > +++ b/kernel/bpf/cgroup.c
> > @@ -1395,7 +1395,7 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> > }
> >
> > out:
> > - if (ret)
> > + if (*kernel_optval == NULL)
> It seems fragile to depend on the caller to init *kernel_optval to NULL.
We can manually reset it to NULL when we enter
__cgroup_bpf_run_filter_setsockopt,
I didn't bother since there is only one existing caller.
But you patch also LGTM, I don't really have a preference.
> How about something like:
>
> diff --git i/kernel/bpf/cgroup.c w/kernel/bpf/cgroup.c
> index 6ec088a96302..8d94c004e781 100644
> --- i/kernel/bpf/cgroup.c
> +++ w/kernel/bpf/cgroup.c
> @@ -1358,7 +1358,7 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
>
> if (copy_from_user(ctx.optval, optval, min(*optlen, max_optlen)) != 0) {
> ret = -EFAULT;
> - goto out;
> + goto err_out;
> }
>
> lock_sock(sk);
> @@ -1368,7 +1368,7 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
>
> if (!ret) {
> ret = -EPERM;
> - goto out;
> + goto err_out;
> }
>
> if (ctx.optlen == -1) {
> @@ -1379,7 +1379,6 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> ret = -EFAULT;
> } else {
> /* optlen within bounds, run kernel handler */
> - ret = 0;
>
> /* export any potential modifications */
> *level = ctx.level;
> @@ -1391,12 +1390,15 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> if (ctx.optlen != 0) {
> *optlen = ctx.optlen;
> *kernel_optval = ctx.optval;
> + } else {
> + sockopt_free_buf(&ctx);
> }
> +
> + return 0;
> }
>
> -out:
> - if (ret)
> - sockopt_free_buf(&ctx);
> +err_out:
> + sockopt_free_buf(&ctx);
> return ret;
> }
