mptcp: Preallocate aligned HMAC key's placeholder

'crypto_hash_setkey' might call a GFP_KERNEL allocation
in case of unaligned input key, causing deadlock.
We can avoid this by preallocating an aligned placeholder for
the key.

Signed-off-by: Fabrizio Demaria <fabrizio.demaria@intel.com>

include/net/mptcp.h

@@ -346,8 +346,11 @@ struct mptcp_cb {
 
 struct mptcp_hmacsha1_pool {
 	struct hash_desc	hmacsha1_desc;
+	u8	*key_placeholder;
 };
 
+#define MPTCP_HMACSHA1_KEYLEN		16
+
 #define MPTCP_SUB_CAPABLE			0
 #define MPTCP_SUB_LEN_CAPABLE_SYN		12
 #define MPTCP_SUB_LEN_CAPABLE_SYN_ALIGN		12

net/ipv4/tcp.c

@@ -443,7 +443,6 @@ void tcp_init_sock(struct sock *sk)
 
 	/* Initialize MPTCP-specific stuff and function-pointers */
 	mptcp_init_tcp_sock(sk);
-	mptcp_alloc_hmacsha1_pool();
 
 	local_bh_disable();
 	sock_update_memcg(sk);

net/mptcp/mptcp_ctrl.c

@@ -391,11 +391,26 @@ static void __mptcp_alloc_hmacsha1_pool(void)
 	for_each_possible_cpu(cpu) {
 		if (!per_cpu(mptcp_hmacsha1_pool, cpu).hmacsha1_desc.tfm) {
 			struct crypto_hash *hash;
+			unsigned int keylen = MPTCP_HMACSHA1_KEYLEN;
+			unsigned long absize;
+			unsigned long alignmask;
+			u8 *buffer;
+			u8 *alignbuffer;
 
+			/* Allocating crypto_hash */
 			hash = crypto_alloc_hash("hmac(sha1)", 0, CRYPTO_ALG_ASYNC);
 			if (IS_ERR_OR_NULL(hash))
 				return;
 			per_cpu(mptcp_hmacsha1_pool, cpu).hmacsha1_desc.tfm = hash;
+
+			/* Allocating aligned key_placeholder */
+			alignmask = crypto_hash_alignmask(hash);
+			absize = keylen + (alignmask & ~(crypto_tfm_ctx_alignment() - 1));
+			buffer = kmalloc(absize, GFP_KERNEL);
+			if (!buffer)
+				return;
+			alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
+			per_cpu(mptcp_hmacsha1_pool, cpu).key_placeholder = alignbuffer;
 		}
 	}
 	/* before setting mptcp_hmacsha1_pool_populated, we must commit all
@@ -489,6 +504,7 @@ void mptcp_disable_static_key(void)
 
 void mptcp_enable_sock(struct sock *sk)
 {
+	mptcp_alloc_hmacsha1_pool();
 	if (!sock_flag(sk, SOCK_MPTCP)) {
 		sock_set_flag(sk, SOCK_MPTCP);
 
@@ -850,7 +866,7 @@ void mptcp_hmac_sha1(u8 *key_1, u8 *key_2, u8 *hash_out, int arg_num, ...)
 {
 	struct mptcp_hmacsha1_pool *sp;
 	struct scatterlist sg;
-	u8 key[16];
+	u8 *key;
 	int i;
 	int length;
 	u8 *msg;
@@ -860,6 +876,7 @@ void mptcp_hmac_sha1(u8 *key_1, u8 *key_2, u8 *hash_out, int arg_num, ...)
 	if (!sp)
 		goto clear_hmac_noput;
 	sp->hmacsha1_desc.flags = 0;
+	key = sp->key_placeholder;
 
 	memcpy(&key[0], key_1, 8);
 	memcpy(&key[8], key_2, 8);