net/rds: fix possible cp null dereference

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net/rds: fix possible cp null dereference cp might be null, calling cp->cp_conn would produce null dereference [Simon Horman adds:] Analysis: * cp is a parameter of __rds_rdma_map and is not reassigned. * The following call-sites pass a NULL cp argument to __rds_rdma_map() - rds_get_mr() - rds_get_mr_for_dest * Prior to the code above, the following assumes that cp may be NULL (which is indicative, but could itself be unnecessary) trans_private = rs->rs_transport->get_mr( sg, nents, rs, &mr->r_key, cp ? cp->cp_conn : NULL, args->vec.addr, args->vec.bytes, need_odp ? ODP_ZEROBASED : ODP_NOT_NEEDED); * The code modified by this patch is guarded by IS_ERR(trans_private), where trans_private is assigned as per the previous point in this analysis. The only implementation of get_mr that I could locate is rds_ib_get_mr() which can return an ERR_PTR if the conn (4th) argument is NULL. * ret is set to PTR_ERR(trans_private). rds_ib_get_mr can return ERR_PTR(-ENODEV) if the conn (4th) argument is NULL. Thus ret may be -ENODEV in which case the code in question will execute. Conclusion: * cp may be NULL at the point where this patch adds a check; this patch does seem to address a possible bug

References

• https://git.kernel.org/stable/c/d275de8ea7be3a453629fddae41d4156762e814c
• https://git.kernel.org/stable/c/bcd46782e2ec3825d10c1552fcb674d491cc09f9
• https://git.kernel.org/stable/c/cfb786b03b03c5ff38882bee38525eb9987e4d14
• https://git.kernel.org/stable/c/d49fac38479bfdaec52b3ea274d290c47a294029
• https://git.kernel.org/stable/c/cbaac2e5488ed54833897264a5ffb2a341a9f196
• https://git.kernel.org/stable/c/92309bed3c5fbe2ccd4c45056efd42edbd06162d
• https://git.kernel.org/stable/c/6794090c742008c53b344b35b021d4a3093dc50a
• https://git.kernel.org/stable/c/62fc3357e079a07a22465b9b6ef71bb6ea75ee4b