Re: [PATCH] RDMA/core: Fix uninitialized gid in ib_nl_process_good_ip_rsep()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Nov 07, 2025 at 04:10:02AM +0000, Kriish Sharma wrote:
> KMSAN reported a use of uninitialized memory in hex_byte_pack()
> via ip6_string() when printing %pI6 from ib_nl_handle_ip_res_resp().
> If the LS_NLA_TYPE_DGID attribute is missing, 'gid' remains
> uninitialized before being used in pr_info(), leading to a
> KMSAN uninit-value report.
> 
> Reported-by: syzbot+938fcd548c303fe33c1a@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=938fcd548c303fe33c1a
> Fixes: ae43f8286730 ("IB/core: Add IP to GID netlink offload")
> Signed-off-by: Kriish Sharma <kriish.sharma2006@gmail.com>
> ---
>  drivers/infiniband/core/addr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
> index 61596cda2b65..4c602fcae12f 100644
> --- a/drivers/infiniband/core/addr.c
> +++ b/drivers/infiniband/core/addr.c
> @@ -99,7 +99,7 @@ static inline bool ib_nl_is_good_ip_resp(const struct nlmsghdr *nlh)
>  static void ib_nl_process_good_ip_rsep(const struct nlmsghdr *nlh)
>  {
>  	const struct nlattr *head, *curr;
> -	union ib_gid gid;
> +	union ib_gid gid = {};
>  	struct addr_req *req;
>  	int len, rem;
>  	int found = 0;

This doesn't seem right.

We have this as the only caller:

	if (ib_nl_is_good_ip_resp(nlh))
		ib_nl_process_good_ip_rsep(nlh);

And ib_nl_is_good_ip_resp() does:

	ret = nla_parse_deprecated(tb, LS_NLA_TYPE_MAX - 1, nlmsg_data(nlh),
				   nlmsg_len(nlh), ib_nl_addr_policy,
				   NULL);

static const struct nla_policy ib_nl_addr_policy[LS_NLA_TYPE_MAX] = {
	[LS_NLA_TYPE_DGID] = {.type = NLA_BINARY,
		.len = sizeof(struct rdma_nla_ls_gid),
		.validation_type = NLA_VALIDATE_MIN,
		.min = sizeof(struct rdma_nla_ls_gid)},
};

So I expect the nla_parse_deprecated() to fail if this:

	nla_for_each_attr(curr, head, len, rem) {
		if (curr->nla_type == LS_NLA_TYPE_DGID)
			memcpy(&gid, nla_data(curr), nla_len(curr));
	}

Doesn't find a DGID.

So how can gid be uninitialized?

The fix to whatever this is should be in ib_nl_is_good_ip_resp().

Jason