net: Properly typecast int values to set sk_max_pacing_rate

In setsockopt(SO_MAX_PACING_RATE) on 64bit systems, sk_max_pacing_rate,
after extended from 'u32' to 'unsigned long', takes unintentionally
hiked value whenever assigned from an 'int' value with MSB=1, due to
binary sign extension in promoting s32 to u64, e.g. 0x80000000 becomes
0xFFFFFFFF80000000.

Thus inflated sk_max_pacing_rate causes subsequent getsockopt to return
~0U unexpectedly. It may also result in increased pacing rate.

Fix by explicitly casting the 'int' value to 'unsigned int' before
assigning it to sk_max_pacing_rate, for zero extension to happen.

Fixes: 76a9ebe ("net: extend sk_pacing_rate to unsigned long")
Signed-off-by: Ji Li <jli@akamai.com>
Signed-off-by: Ke Li <keli@akamai.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20201022064146.79873-1-keli@akamai.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: okisme25

net/core/filter.c

@@ -4733,7 +4733,8 @@ static int _bpf_setsockopt(struct sock *sk, int level, int optname,
 				cmpxchg(&sk->sk_pacing_status,
 					SK_PACING_NONE,
 					SK_PACING_NEEDED);
-			sk->sk_max_pacing_rate = (val == ~0U) ? ~0UL : val;
+			sk->sk_max_pacing_rate = (val == ~0U) ?
+						 ~0UL : (unsigned int)val;
 			sk->sk_pacing_rate = min(sk->sk_pacing_rate,
 						 sk->sk_max_pacing_rate);
 			break;

net/core/sock.c

@@ -1163,7 +1163,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 
 	case SO_MAX_PACING_RATE:
 		{
-		unsigned long ulval = (val == ~0U) ? ~0UL : val;
+		unsigned long ulval = (val == ~0U) ? ~0UL : (unsigned int)val;
 
 		if (sizeof(ulval) != sizeof(val) &&
 		    optlen >= sizeof(ulval) &&