[PATCH v2 net 1/2] net: restrict SO_RESERVE_MEM to TCP sockets and cap max value

[Eric Dumazet <edumazet@google.com>]

Commit 2bb2f5fb21b0 ("net: add new socket option SO_RESERVE_MEM") and
commit d00c8ee31729 ("net: fix possible NULL deref in sock_reserve_memory")
only checked sk_has_account(sk), which is true for both TCP and UDP
sockets.

However, SO_RESERVE_MEM and sk_unused_reserved_mem() are currently only
supported by TCP:
- On UDP sockets, sk->sk_forward_alloc is protected by
  sk->sk_receive_queue.lock, whereas sock_reserve_memory() and
  sock_release_reserved_memory() only acquire lock_sock(sk). Concurrent
  UDP packet reception/release and setsockopt(SO_RESERVE_MEM) corrupt
  sk_forward_alloc and memcg accounting.
- udp_rmem_release() reclaims excess sk_forward_alloc without
  accounting for sk_unused_reserved_mem(sk).

Restrict sock_reserve_memory() to TCP sockets (sk_is_tcp(sk)) for now.
Supporting SO_RESERVE_MEM for UDP (acquiring sk_receive_queue.lock and
honoring sk_unused_reserved_mem() in udp_rmem_release()) can be done in
a future net-next series if needed.

In addition, reject val > SZ_1G with -EINVAL in
sk_setsockopt(SO_RESERVE_MEM). Without an upper bound, values near
INT_MAX cause sk_mem_pages(delta) and (pages << PAGE_SHIFT) to overflow
32-bit signed int, corrupting sk->sk_forward_alloc and
sk->sk_reserved_mem. Using a page-aligned cap (SZ_1G) ensures that the
page-rounded sk->sk_reserved_mem reported by getsockopt(SO_RESERVE_MEM)
can always be passed back to setsockopt(SO_RESERVE_MEM).

Fixes: 2bb2f5fb21b0 ("net: add new socket option SO_RESERVE_MEM")
Reported-by: Cai Xinchen <caixinchen1@huawei.com>
Closes: https://lore.kernel.org/netdev/5a88421d-10ef-4fca-9acb-85a27a3c1173@huawei.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Wei Wang <weiwan@google.com>
---
 net/core/sock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index d23333bb4f3fafa19f58095522ef10d918d92496..e8551df8330ff4b1d662b0d0133e20d1f74eb728 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1034,7 +1034,7 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 	bool charged;
 	int pages;
 
-	if (!mem_cgroup_sk_enabled(sk) || !sk_has_account(sk))
+	if (!mem_cgroup_sk_enabled(sk) || !sk_is_tcp(sk))
 		return -EOPNOTSUPP;
 
 	if (!bytes)
@@ -1661,7 +1661,7 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 	{
 		int delta;
 
-		if (val < 0) {
+		if (val < 0 || val > SZ_1G) {
 			ret = -EINVAL;
 			break;
 		}
-- 
2.56.0.rc1.315.gc6ed9934b7-goog