netdev - [PATCH net] ethtool: fix string set id check

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Message-Id: <b54ed5c5fd972a59afea3e1badfb36d86df68799.1607952208.git.mkubecek@suse.cz>
Date:   Mon, 14 Dec 2020 14:25:01 +0100 (CET)
From:   Michal Kubecek <mkubecek@...e.cz>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH net] ethtool: fix string set id check

Syzbot reported a shift of a u32 by more than 31 in strset_parse_request()
which is undefined behavior. This is caused by range check of string set id
using variable ret (which is always 0 at this point) instead of id (string
set id from request).

Fixes: 71921690f974 ("ethtool: provide string sets with STRSET_GET request")
Reported-by: syzbot+96523fb438937cd01220@...kaller.appspotmail.com
Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
---
 net/ethtool/strset.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/strset.c b/net/ethtool/strset.c
index 0baad0ce1832..c3a5489964cd 100644
--- a/net/ethtool/strset.c
+++ b/net/ethtool/strset.c
@@ -182,7 +182,7 @@ static int strset_parse_request(struct ethnl_req_info *req_base,
 		ret = strset_get_id(attr, &id, extack);
 		if (ret < 0)
 			return ret;
-		if (ret >= ETH_SS_COUNT) {
+		if (id >= ETH_SS_COUNT) {
 			NL_SET_ERR_MSG_ATTR(extack, attr,
 					    "unknown string set id");
 			return -EOPNOTSUPP;
-- 
2.29.2