Re: [PATCH] IB/mlx5: Fix a possible null-pointer dereference in set_roce_addr()

[Tuo Li]

Hi Michael,

On Mon, Dec 15, 2025 at 5:42 PM Michael Gur <michaelgur@xxxxxxxxxx> wrote:
>
>
> On 12/9/2025 9:23 AM, Tuo Li wrote:
> > The pointer gid is checked at the beginning of set_roce_addr(). However,
> > if it is NULL, the function continues execution and may dereference gid
> > when calling mlx5_core_roce_gid_set():
> >
> >    return mlx5_core_roce_gid_set(..., gid->raw, ...)
> >
> > This can lead to a null-pointer dereference. To prevent this, add an else
> > branch that return -EINVAL when gid is NULL, and remove the redundant gid
> > check in the IB_GID_TYPE_ROCE_UDP_ENCAP case.
>
> Can you reproduce this?
>
> Theoretically, gid->raw is translated to NULL+0 which is undefined
> behavior and static analyzers can complain, but it seems compilers just
> translate to NULL which leads us to the expected behavior.
>
> > Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
> > ---
> >   drivers/infiniband/hw/mlx5/main.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> > index 40284bbb45d6..d68a58d249d4 100644
> > --- a/drivers/infiniband/hw/mlx5/main.c
> > +++ b/drivers/infiniband/hw/mlx5/main.c
> > @@ -645,6 +645,8 @@ int set_roce_addr(struct mlx5_ib_dev *dev, u32 port_num,
> >               ret = rdma_read_gid_l2_fields(attr, &vlan_id, &mac[0]);
> >               if (ret)
> >                       return ret;
> > +     } else {
> > +             return -EINVAL;
> >       }
>
> This breaks the gid deletion, we should still call mlx5_core with NULL
> gid for it to update the table.
>
> >
> >       switch (gid_type) {
> > @@ -653,7 +655,7 @@ int set_roce_addr(struct mlx5_ib_dev *dev, u32 port_num,
> >               break;
> >       case IB_GID_TYPE_ROCE_UDP_ENCAP:
> >               roce_version = MLX5_ROCE_VERSION_2;
> > -             if (gid && ipv6_addr_v4mapped((void *)gid))
> > +             if (ipv6_addr_v4mapped((void *)gid))
> >                       roce_l3_type = MLX5_ROCE_L3_TYPE_IPV4;
> >               else
> >                       roce_l3_type = MLX5_ROCE_L3_TYPE_IPV6;

I have rechecked the code. In this case, accessing the first member of a
NULL pointer is safe. Moreover, mlx5_core_roce_gid_set() also checks
gid->raw before using it, so an early return is not necessary.

Thanks for your feedback, and sorry for any inconvenience caused.