netdev - [PATCH v1 net] netlink: Use copy_to_user() for optval in netlink

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Date:   Tue, 18 Apr 2023 17:42:46 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
CC:     Patrick McHardy <kaber@...sh.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Christophe Ricard <christophe-h.ricard@...com>,
        Johannes Berg <johannes.berg@...el.com>,
        David Ahern <dsahern@...il.com>,
        Kuniyuki Iwashima <kuniyu@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        <netdev@...r.kernel.org>, Brad Spencer <bspencer@...ckberry.com>
Subject: [PATCH v1 net] netlink: Use copy_to_user() for optval in netlink_getsockopt().

Brad Spencer provided a detailed report that when calling getsockopt()
for AF_NETLINK, some SOL_NETLINK options set only 1 byte even though such
options require more than int as length.

The options return a flag value that fits into 1 byte, but such behaviour
confuses users who do not strictly check the value as char.

Currently, netlink_getsockopt() uses put_user() to copy data to optlen and
optval, but put_user() casts the data based on the pointer, char *optval.
So, only 1 byte is set to optval.

To avoid this behaviour, we need to use copy_to_user() or cast optval for
put_user().

Now getsockopt() accepts char as optval as the flags are only 1 byte.

Fixes: 9a4595bc7e67 ("[NETLINK]: Add set/getsockopt options to support more than 32 groups")
Fixes: be0c22a46cfb ("netlink: add NETLINK_BROADCAST_ERROR socket option")
Fixes: 38938bfe3489 ("netlink: add NETLINK_NO_ENOBUFS socket flag")
Fixes: 0a6a3a23ea6e ("netlink: add NETLINK_CAP_ACK socket option")
Fixes: 2d4bc93368f5 ("netlink: extended ACK reporting")
Fixes: 89d35528d17d ("netlink: Add new socket option to enable strict checking on dumps")
Reported-by: Brad Spencer <bspencer@...ckberry.com>
Link: https://lore.kernel.org/netdev/ZD7VkNWFfp22kTDt@datsun.rim.net/
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/netlink/af_netlink.c | 56 +++++++---------------------------------
 1 file changed, 10 insertions(+), 46 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index f365dfdd672d..3106f09d5f1c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1742,7 +1742,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 {
 	struct sock *sk = sock->sk;
 	struct netlink_sock *nlk = nlk_sk(sk);
-	int len, val, err;
+	int len, val;
 
 	if (level != SOL_NETLINK)
 		return -ENOPROTOOPT;
@@ -1754,39 +1754,17 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 
 	switch (optname) {
 	case NETLINK_PKTINFO:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
 		val = nlk->flags & NETLINK_F_RECV_PKTINFO ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
 		break;
 	case NETLINK_BROADCAST_ERROR:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
 		val = nlk->flags & NETLINK_F_BROADCAST_SEND_ERROR ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
 		break;
 	case NETLINK_NO_ENOBUFS:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
 		val = nlk->flags & NETLINK_F_RECV_NO_ENOBUFS ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
 		break;
 	case NETLINK_LIST_MEMBERSHIPS: {
-		int pos, idx, shift;
+		int pos, idx, shift, err = 0;
 
-		err = 0;
 		netlink_lock_table();
 		for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) {
 			if (len - pos < sizeof(u32))
@@ -1803,40 +1781,26 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
 		if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen))
 			err = -EFAULT;
 		netlink_unlock_table();
-		break;
+		return err;
 	}
 	case NETLINK_CAP_ACK:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
 		val = nlk->flags & NETLINK_F_CAP_ACK ? 1 : 0;
-		if (put_user(len, optlen) ||
-		    put_user(val, optval))
-			return -EFAULT;
-		err = 0;
 		break;
 	case NETLINK_EXT_ACK:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
 		val = nlk->flags & NETLINK_F_EXT_ACK ? 1 : 0;
-		if (put_user(len, optlen) || put_user(val, optval))
-			return -EFAULT;
-		err = 0;
 		break;
 	case NETLINK_GET_STRICT_CHK:
-		if (len < sizeof(int))
-			return -EINVAL;
-		len = sizeof(int);
 		val = nlk->flags & NETLINK_F_STRICT_CHK ? 1 : 0;
-		if (put_user(len, optlen) || put_user(val, optval))
-			return -EFAULT;
-		err = 0;
 		break;
 	default:
-		err = -ENOPROTOOPT;
+		return -ENOPROTOOPT;
 	}
-	return err;
+
+	if (put_user(len, optlen) ||
+	    copy_to_user(optval, &val, len))
+		return -EFAULT;
+
+	return 0;
 }
 
 static void netlink_cmsg_recv_pktinfo(struct msghdr *msg, struct sk_buff *skb)
-- 
2.30.2