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

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@blackberry.com>
Link: https://lore.kernel.org/netdev/ZD7VkNWFfp22kTDt@datsun.rim.net/
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Link: https://lore.kernel.org/r/20230421185255.94606-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index f365dfd..9b6eb28 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1742,7 +1742,8 @@ 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;
@@ -1754,39 +1755,17 @@ 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))
@@ -1803,40 +1782,32 @@ 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)