Re: [PATCH v2] RDMA/core: Check for missing DGID attribute in ib_nl_is_good_ip_resp()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Sat, Nov 08, 2025 at 03:43:36AM +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().
> Previously, ib_nl_process_good_ip_rsep() used the 'gid' without
> verifying that the LS_NLA_TYPE_DGID attribute was present.
> 
> This patch adds a check for the DGID attribute in ib_nl_is_good_ip_resp(),
> returning false if it is missing. This prevents uninitialized memory
> usage downstream in ib_nl_process_good_ip_rsep().
> 
> Suggested-by: Vlad Dumitrescu <vdumitrescu@nvidia.com>
> 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>
> ---
> v2:
>  - Added check for LS_NLA_TYPE_DGID in ib_nl_is_good_ip_resp() to
>    avoid uninitialized 'gid' usage, as suggested by Vlad Dumitrescu.
> 
> v1: https://lore.kernel.org/all/20251107041002.2091584-1-kriish.sharma2006@gmail.com
> 
>  drivers/infiniband/core/addr.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

> diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
> index 61596cda2b65..dde9114fe6a1 100644
> --- a/drivers/infiniband/core/addr.c
> +++ b/drivers/infiniband/core/addr.c
> @@ -93,13 +93,16 @@ static inline bool ib_nl_is_good_ip_resp(const struct nlmsghdr *nlh)
>  	if (ret)
>  		return false;
>  
> +	if (!tb[LS_NLA_TYPE_DGID])
> +		return false;
> +
>  	return true;
>  }
>  
>  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 = {};

Let's drop this.

Looking at the whole flow, it looks like it is not using
nla_parse_deprecated properly.. I think it should look like this which
will fix the issue and make it run faster:

diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
index 61596cda2b65f3..35ba852a172aad 100644
--- a/drivers/infiniband/core/addr.c
+++ b/drivers/infiniband/core/addr.c
@@ -80,37 +80,25 @@ static const struct nla_policy ib_nl_addr_policy[LS_NLA_TYPE_MAX] = {
 		.min = sizeof(struct rdma_nla_ls_gid)},
 };
 
-static inline bool ib_nl_is_good_ip_resp(const struct nlmsghdr *nlh)
+static void ib_nl_process_ip_rsep(const struct nlmsghdr *nlh)
 {
 	struct nlattr *tb[LS_NLA_TYPE_MAX] = {};
+	union ib_gid gid;
+	struct addr_req *req;
+	int found = 0;
 	int ret;
 
 	if (nlh->nlmsg_flags & RDMA_NL_LS_F_ERR)
-		return false;
+		return;
 
 	ret = nla_parse_deprecated(tb, LS_NLA_TYPE_MAX - 1, nlmsg_data(nlh),
 				   nlmsg_len(nlh), ib_nl_addr_policy, NULL);
 	if (ret)
-		return false;
+		return;
 
-	return true;
-}
-
-static void ib_nl_process_good_ip_rsep(const struct nlmsghdr *nlh)
-{
-	const struct nlattr *head, *curr;
-	union ib_gid gid;
-	struct addr_req *req;
-	int len, rem;
-	int found = 0;
-
-	head = (const struct nlattr *)nlmsg_data(nlh);
-	len = nlmsg_len(nlh);
-
-	nla_for_each_attr(curr, head, len, rem) {
-		if (curr->nla_type == LS_NLA_TYPE_DGID)
-			memcpy(&gid, nla_data(curr), nla_len(curr));
-	}
+	if (!tb[LS_NLA_TYPE_DGID])
+		return;
+	memcpy(&gid, nla_data(tb[LS_NLA_TYPE_DGID]), sizeof(gid));
 
 	spin_lock_bh(&lock);
 	list_for_each_entry(req, &req_list, list) {
@@ -137,8 +125,7 @@ int ib_nl_handle_ip_res_resp(struct sk_buff *skb,
 	    !(NETLINK_CB(skb).sk))
 		return -EPERM;
 
-	if (ib_nl_is_good_ip_resp(nlh))
-		ib_nl_process_good_ip_rsep(nlh);
+	ib_nl_process_ip_rsep(nlh);
 
 	return 0;
 }