On Wed, May 18, 2022 at 04:30:14PM -0700, Andrii Nakryiko wrote:
> 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?
Just to avoid double calculation of size, otherwise I don't have
any significant prefernce, other than -EOVERFLOW would not be reported
separately (not sure if this a good or a bad thing), and that
it would be a bit more cumbersome to incorporate the Yonghong's
suggestion[1] about the INT_MAX check.
[1] https://lore.kernel.org/lkml/412bf136-6a5b-f442-1e84-778697e2b694@xxxxxx/
> > if (!addrs)
> > return -ENOMEM;
> > --
> > 2.1.4
> >
>
