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From:   Michal Kubecek <mkubecek@suse.cz>
Subject: [PATCH net v2] netlink: check for null extack in cookie helpers
To:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org
Cc:     Johannes Berg <johannes@sipsolutions.net>,
        linux-kernel@vger.kernel.org
Message-Id: <20200320234650.E3383E0FD3@unicorn.suse.cz>
Date:   Sat, 21 Mar 2020 00:46:50 +0100 (CET)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Unlike NL_SET_ERR_* macros, nl_set_extack_cookie_u64() and
nl_set_extack_cookie_u32() helpers do not check extack argument for null
and neither do their callers, as syzbot recently discovered for
ethnl_parse_header().

Instead of fixing the callers and leaving the trap in place, add check of
null extack to both helpers to make them consistent with NL_SET_ERR_*
macros.

v2: drop incorrect second Fixes tag

Fixes: 2363d73a2f3e ("ethtool: reject unrecognized request flags")
Reported-by: syzbot+258a9089477493cea67b@syzkaller.appspotmail.com
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
---
 include/linux/netlink.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 4090524c3462..60739d0cbf93 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -115,6 +115,8 @@ static inline void nl_set_extack_cookie_u64(struct netlink_ext_ack *extack,
 {
 	u64 __cookie = cookie;
 
+	if (!extack)
+		return;
 	memcpy(extack->cookie, &__cookie, sizeof(__cookie));
 	extack->cookie_len = sizeof(__cookie);
 }
@@ -124,6 +126,8 @@ static inline void nl_set_extack_cookie_u32(struct netlink_ext_ack *extack,
 {
 	u32 __cookie = cookie;
 
+	if (!extack)
+		return;
 	memcpy(extack->cookie, &__cookie, sizeof(__cookie));
 	extack->cookie_len = sizeof(__cookie);
 }
-- 
2.25.1