tcp: md5: use kmalloc() backed scratch areas

Some arches have virtually mapped kernel stacks, or will soon have.

tcp_md5_hash_header() uses an automatic variable to copy tcp header
before mangling th->check and calling crypto function, which might
be problematic on such arches.

David says that using percpu storage is also problematic on non SMP
builds.

Just use kmalloc() to allocate scratch areas.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 40 insertions, 30 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 108ef2a..032a96d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3026,8 +3026,18 @@ static void __tcp_alloc_md5sig_pool(void)
 		return;
 
 	for_each_possible_cpu(cpu) {
+		void *scratch = per_cpu(tcp_md5sig_pool, cpu).scratch;
 		struct ahash_request *req;
 
+		if (!scratch) {
+			scratch = kmalloc_node(sizeof(union tcp_md5sum_block) +
+					       sizeof(struct tcphdr),
+					       GFP_KERNEL,
+					       cpu_to_node(cpu));
+			if (!scratch)
+				return;
+			per_cpu(tcp_md5sig_pool, cpu).scratch = scratch;
+		}
 		if (per_cpu(tcp_md5sig_pool, cpu).md5_req)
 			continue;
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3708de2..32b048e 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1018,27 +1018,28 @@ static int tcp_v4_parse_md5_keys(struct sock *sk, char __user *optval,
 			      GFP_KERNEL);
 }
 
-static int tcp_v4_md5_hash_pseudoheader(struct tcp_md5sig_pool *hp,
-					__be32 daddr, __be32 saddr, int nbytes)
+static int tcp_v4_md5_hash_headers(struct tcp_md5sig_pool *hp,
+				   __be32 daddr, __be32 saddr,
+				   const struct tcphdr *th, int nbytes)
 {
 	struct tcp4_pseudohdr *bp;
 	struct scatterlist sg;
+	struct tcphdr *_th;
 
-	bp = &hp->md5_blk.ip4;
-
-	/*
-	 * 1. the TCP pseudo-header (in the order: source IP address,
-	 * destination IP address, zero-padded protocol number, and
-	 * segment length)
-	 */
+	bp = hp->scratch;
 	bp->saddr = saddr;
 	bp->daddr = daddr;
 	bp->pad = 0;
 	bp->protocol = IPPROTO_TCP;
 	bp->len = cpu_to_be16(nbytes);
 
-	sg_init_one(&sg, bp, sizeof(*bp));
-	ahash_request_set_crypt(hp->md5_req, &sg, NULL, sizeof(*bp));
+	_th = (struct tcphdr *)(bp + 1);
+	memcpy(_th, th, sizeof(*th));
+	_th->check = 0;
+
+	sg_init_one(&sg, bp, sizeof(*bp) + sizeof(*th));
+	ahash_request_set_crypt(hp->md5_req, &sg, NULL,
+				sizeof(*bp) + sizeof(*th));
 	return crypto_ahash_update(hp->md5_req);
 }
 
@@ -1055,9 +1056,7 @@ static int tcp_v4_md5_hash_hdr(char *md5_hash, const struct tcp_md5sig_key *key,
 
 	if (crypto_ahash_init(req))
 		goto clear_hash;
-	if (tcp_v4_md5_hash_pseudoheader(hp, daddr, saddr, th->doff << 2))
-		goto clear_hash;
-	if (tcp_md5_hash_header(hp, th))
+	if (tcp_v4_md5_hash_headers(hp, daddr, saddr, th, th->doff << 2))
 		goto clear_hash;
 	if (tcp_md5_hash_key(hp, key))
 		goto clear_hash;
@@ -1101,9 +1100,7 @@ int tcp_v4_md5_hash_skb(char *md5_hash, const struct tcp_md5sig_key *key,
 	if (crypto_ahash_init(req))
 		goto clear_hash;
 
-	if (tcp_v4_md5_hash_pseudoheader(hp, daddr, saddr, skb->len))
-		goto clear_hash;
-	if (tcp_md5_hash_header(hp, th))
+	if (tcp_v4_md5_hash_headers(hp, daddr, saddr, th, skb->len))
 		goto clear_hash;
 	if (tcp_md5_hash_skb_data(hp, skb, th->doff << 2))
 		goto clear_hash;
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 2255d2b..37cf913 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -526,26 +526,33 @@ static int tcp_v6_parse_md5_keys(struct sock *sk, char __user *optval,
 			      AF_INET6, cmd.tcpm_key, cmd.tcpm_keylen, GFP_KERNEL);
 }
 
-static int tcp_v6_md5_hash_pseudoheader(struct tcp_md5sig_pool *hp,
-					const struct in6_addr *daddr,
-					const struct in6_addr *saddr, int nbytes)
+static int tcp_v6_md5_hash_headers(struct tcp_md5sig_pool *hp,
+				   const struct in6_addr *daddr,
+				   const struct in6_addr *saddr,
+				   const struct tcphdr *th, int nbytes)
 {
 	struct tcp6_pseudohdr *bp;
 	struct scatterlist sg;
+	struct tcphdr *_th;
 
-	bp = &hp->md5_blk.ip6;
+	bp = hp->scratch;
 	/* 1. TCP pseudo-header (RFC2460) */
 	bp->saddr = *saddr;
 	bp->daddr = *daddr;
 	bp->protocol = cpu_to_be32(IPPROTO_TCP);
 	bp->len = cpu_to_be32(nbytes);
 
-	sg_init_one(&sg, bp, sizeof(*bp));
-	ahash_request_set_crypt(hp->md5_req, &sg, NULL, sizeof(*bp));
+	_th = (struct tcphdr *)(bp + 1);
+	memcpy(_th, th, sizeof(*th));
+	_th->check = 0;
+
+	sg_init_one(&sg, bp, sizeof(*bp) + sizeof(*th));
+	ahash_request_set_crypt(hp->md5_req, &sg, NULL,
+				sizeof(*bp) + sizeof(*th));
 	return crypto_ahash_update(hp->md5_req);
 }
 
-static int tcp_v6_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,
+static int tcp_v6_md5_hash_hdr(char *md5_hash, const struct tcp_md5sig_key *key,
 			       const struct in6_addr *daddr, struct in6_addr *saddr,
 			       const struct tcphdr *th)
 {
@@ -559,9 +566,7 @@ static int tcp_v6_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,
 
 	if (crypto_ahash_init(req))
 		goto clear_hash;
-	if (tcp_v6_md5_hash_pseudoheader(hp, daddr, saddr, th->doff << 2))
-		goto clear_hash;
-	if (tcp_md5_hash_header(hp, th))
+	if (tcp_v6_md5_hash_headers(hp, daddr, saddr, th, th->doff << 2))
 		goto clear_hash;
 	if (tcp_md5_hash_key(hp, key))
 		goto clear_hash;
@@ -606,9 +611,7 @@ static int tcp_v6_md5_hash_skb(char *md5_hash,
 	if (crypto_ahash_init(req))
 		goto clear_hash;
 
-	if (tcp_v6_md5_hash_pseudoheader(hp, daddr, saddr, skb->len))
-		goto clear_hash;
-	if (tcp_md5_hash_header(hp, th))
+	if (tcp_v6_md5_hash_headers(hp, daddr, saddr, th, skb->len))
 		goto clear_hash;
 	if (tcp_md5_hash_skb_data(hp, skb, th->doff << 2))
 		goto clear_hash;