net: fix SO_DEVMEM_DONTNEED looping too long

Exit early if we're freeing more than 1024 frags, to prevent
looping too long.

Also minor code cleanups:
- Flip checks to reduce indentation.
- Use sizeof(*tokens) everywhere for consistentcy.

Cc: Yi Lai <yi1.lai@linux.intel.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20241107210331.3044434-1-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: mina

net/core/sock.c

@@ -1052,32 +1052,34 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 
 #ifdef CONFIG_PAGE_POOL
 
-/* This is the number of tokens that the user can SO_DEVMEM_DONTNEED in
- * 1 syscall. The limit exists to limit the amount of memory the kernel
- * allocates to copy these tokens.
+/* This is the number of tokens and frags that the user can SO_DEVMEM_DONTNEED
+ * in 1 syscall. The limit exists to limit the amount of memory the kernel
+ * allocates to copy these tokens, and to prevent looping over the frags for
+ * too long.
  */
 #define MAX_DONTNEED_TOKENS 128
+#define MAX_DONTNEED_FRAGS 1024
 
 static noinline_for_stack int
 sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
 {
 	unsigned int num_tokens, i, j, k, netmem_num = 0;
 	struct dmabuf_token *tokens;
+	int ret = 0, num_frags = 0;
 	netmem_ref netmems[16];
-	int ret = 0;
 
 	if (!sk_is_tcp(sk))
 		return -EBADF;
 
-	if (optlen % sizeof(struct dmabuf_token) ||
+	if (optlen % sizeof(*tokens) ||
 	    optlen > sizeof(*tokens) * MAX_DONTNEED_TOKENS)
 		return -EINVAL;
 
-	tokens = kvmalloc_array(optlen, sizeof(*tokens), GFP_KERNEL);
+	num_tokens = optlen / sizeof(*tokens);
+	tokens = kvmalloc_array(num_tokens, sizeof(*tokens), GFP_KERNEL);
 	if (!tokens)
 		return -ENOMEM;
 
-	num_tokens = optlen / sizeof(struct dmabuf_token);
 	if (copy_from_sockptr(tokens, optval, optlen)) {
 		kvfree(tokens);
 		return -EFAULT;
@@ -1086,24 +1088,28 @@ sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
 	xa_lock_bh(&sk->sk_user_frags);
 	for (i = 0; i < num_tokens; i++) {
 		for (j = 0; j < tokens[i].token_count; j++) {
+			if (++num_frags > MAX_DONTNEED_FRAGS)
+				goto frag_limit_reached;
+
 			netmem_ref netmem = (__force netmem_ref)__xa_erase(
 				&sk->sk_user_frags, tokens[i].token_start + j);
 
-			if (netmem &&
-			    !WARN_ON_ONCE(!netmem_is_net_iov(netmem))) {
-				netmems[netmem_num++] = netmem;
-				if (netmem_num == ARRAY_SIZE(netmems)) {
-					xa_unlock_bh(&sk->sk_user_frags);
-					for (k = 0; k < netmem_num; k++)
-						WARN_ON_ONCE(!napi_pp_put_page(netmems[k]));
-					netmem_num = 0;
-					xa_lock_bh(&sk->sk_user_frags);
-				}
-				ret++;
+			if (!netmem || WARN_ON_ONCE(!netmem_is_net_iov(netmem)))
+				continue;
+
+			netmems[netmem_num++] = netmem;
+			if (netmem_num == ARRAY_SIZE(netmems)) {
+				xa_unlock_bh(&sk->sk_user_frags);
+				for (k = 0; k < netmem_num; k++)
+					WARN_ON_ONCE(!napi_pp_put_page(netmems[k]));
+				netmem_num = 0;
+				xa_lock_bh(&sk->sk_user_frags);
 			}
+			ret++;
 		}
 	}
 
+frag_limit_reached:
 	xa_unlock_bh(&sk->sk_user_frags);
 	for (k = 0; k < netmem_num; k++)
 		WARN_ON_ONCE(!napi_pp_put_page(netmems[k]));