Patch "netlink: Use copy_to_user() for optval in netlink_getsockopt()." has been added to the 5.15-stable tree

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This is a note to let you know that I've just added the patch titled

    netlink: Use copy_to_user() for optval in netlink_getsockopt().

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netlink-use-copy_to_user-for-optval-in-netlink_getso.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 58396c57d995ecc745240bdd75c2fb04c862ad4c
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Fri Apr 21 11:52:55 2023 -0700

    netlink: Use copy_to_user() for optval in netlink_getsockopt().
    
    [ Upstream commit d913d32cc2707e9cd24fe6fa6d7d470e9c728980 ]
    
    Brad Spencer provided a detailed report [0] that when calling getsockopt()
    for AF_NETLINK, some SOL_NETLINK options set only 1 byte even though such
    options require at least sizeof(int) as length.
    
    The options return a flag value that fits into 1 byte, but such behaviour
    confuses users who do not initialise the variable before calling
    getsockopt() and do not strictly check the returned 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.
    As a result, only 1 byte is set to optval.
    
    To avoid this behaviour, we need to use copy_to_user() or cast optval for
    put_user().
    
    Note that this changes the behaviour on big-endian systems, but we document
    that the size of optval is int in the man page.
    
      $ man 7 netlink
      ...
      Socket options
           To set or get a netlink socket option, call getsockopt(2) to read
           or setsockopt(2) to write the option with the option level argument
           set to SOL_NETLINK.  Unless otherwise noted, optval is a pointer to
           an int.
    
    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@xxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/netdev/ZD7VkNWFfp22kTDt@xxxxxxxxxxxxxx/
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Reviewed-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230421185255.94606-1-kuniyu@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 011ec7d9a719e..84a7a29be49d8 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1752,7 +1752,8 @@ 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;
+	unsigned int flag;
+	int len, val;
 
 	if (level != SOL_NETLINK)
 		return -ENOPROTOOPT;
@@ -1764,39 +1765,17 @@ 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;
+		flag = NETLINK_F_RECV_PKTINFO;
 		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;
+		flag = NETLINK_F_BROADCAST_SEND_ERROR;
 		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;
+		flag = NETLINK_F_RECV_NO_ENOBUFS;
 		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))
@@ -1813,40 +1792,32 @@ 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;
+		flag = NETLINK_F_CAP_ACK;
 		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;
+		flag = NETLINK_F_EXT_ACK;
 		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;
+		flag = NETLINK_F_STRICT_CHK;
 		break;
 	default:
-		err = -ENOPROTOOPT;
+		return -ENOPROTOOPT;
 	}
-	return err;
+
+	if (len < sizeof(int))
+		return -EINVAL;
+
+	len = sizeof(int);
+	val = nlk->flags & flag ? 1 : 0;
+
+	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)



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