On Sat, Feb 23, 2019 at 12:48:53PM -0800, Eric Dumazet wrote:
>
>
> On 02/23/2019 12:38 PM, Alexei Starovoitov wrote:
> > On Sat, Feb 23, 2019 at 11:07:09AM -0800, Eric Dumazet wrote:
> >> If caller of bpf_setsockopt() is silly passing a negative optlen
> >> bad things happen.
> >>
> >> Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control")
> >> Signed-off-by: Eric Dumazet <[email protected]>
> >> Cc: Lawrence Brakmo <[email protected]>
> >> ---
> >> net/core/filter.c | 5 +++--
> >> 1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/net/core/filter.c b/net/core/filter.c
> >> index
> >> f7d0004fc16096eb42ece3a6acf645540ee2326b..6a5d89464168f2f35f43986c1dbc0446c9390a3c
> >> 100644
> >> --- a/net/core/filter.c
> >> +++ b/net/core/filter.c
> >> @@ -4194,8 +4194,9 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern
> >> *, bpf_sock,
> >> char name[TCP_CA_NAME_MAX];
> >> bool reinit = bpf_sock->op > BPF_SOCK_OPS_NEEDS_ECN;
> >>
> >> - strncpy(name, optval, min_t(long, optlen,
> >> - TCP_CA_NAME_MAX-1));
> >> + if (optlen < 0)
> >> + return -EINVAL;
> >> + strncpy(name, optval, min(optlen, TCP_CA_NAME_MAX - 1));
> >
> > Unnecessary.
> > The verifier guarantees that optlen > 0 because
> > static const struct bpf_func_proto bpf_setsockopt_proto = {
> > .func = bpf_setsockopt,
> > ...
> > .arg5_type = ARG_CONST_SIZE,
> > };
> >
>
> Even on 32bit kernel ?
>
> The suspect thing to me is the min_t(long, ....)
>
> optlen is an integer, why do we need to promote to a long ?
I think the code is actually fine as-is.
I bet it was copy pasted from do_tcp_setsockopt
where similar min_t(long) is used to match strncpy_from_user() declaration.
Here min_t(long) or min_t(int) or min() doesn't matter.
I would keep it as-is to avoid noisy patches.
