On Mon, Jan 11, 2021 at 02:38:02PM -0800, Stanislav Fomichev wrote:
> 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,
It feels weird to reset the caller value at the beginning while this is not
intended to be an _init() like function, so I avoided it.
but yeah, I am fine on this way also and won't oppose it strongly ;)
> 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;
> > }
