[PATCH v2 net-next] tcp: md5: use kmalloc() backed scratch areas

[Eric Dumazet <eric.dumazet@gmail.com>]

From: Eric Dumazet <edumazet@google.com>

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>
---
 include/net/tcp.h   |    3 +--
 net/ipv4/tcp.c      |   10 ++++++++++
 net/ipv4/tcp_ipv4.c |   31 ++++++++++++++-----------------
 net/ipv6/tcp_ipv6.c |   29 ++++++++++++++++-------------
 4 files changed, 41 insertions(+), 32 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a79894b667265cdf9e3fe793b4757e2f932b378a..7d892f65d6c88a4520e4e2a9695478e0e8a7a7f7 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1384,7 +1384,7 @@ union tcp_md5sum_block {
 /* - pool: digest algorithm, hash description and scratch buffer */
 struct tcp_md5sig_pool {
 	struct ahash_request	*md5_req;
-	union tcp_md5sum_block	md5_blk;
+	void			*scratch;
 };
 
 /* - functions */
@@ -1420,7 +1420,6 @@ static inline void tcp_put_md5sig_pool(void)
 	local_bh_enable();
 }
 
-int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
 int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,
 			  unsigned int header_len);
 int tcp_md5_hash_key(struct tcp_md5sig_pool *hp,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 5c7ed147449c1b7ba029b12e033ad779a631460a..fddc0ab799996c1df82cb05dba03271b773e3b2d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2969,8 +2969,18 @@ 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 3708de2a66833cf1d4a221a2b6ce3923bde978c4..32b048e524d6773538918eca175b3f422f9c2aa7 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 f36c2d076fce0df30d202d7683a67e3614d77fe9..bf3556f1808fd4e625c9c4b69431d2ee22463f5e 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;