rxrpc: Reuse SKCIPHER_REQUEST_ON_STACK buffer

PATCH In review Kees Cook 3 participants 5 messages Jul 16, 2018 – Jul 19, 2018

Subsystems (3)

Networking Network drivers Rxrpc sockets (AF_RXRPC)

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Kees Cook

author

2018-07-16 03:49 UTC #0 lore raw

PATCH 1/1 rxrpc: Reuse SKCIPHER_REQUEST_ON_STACK buffer

The use of SKCIPHER_REQUEST_ON_STACK() will trigger FRAME_WARN warnings (when less than 2048) once the VLA is no longer hidden from the check:

net/rxrpc/rxkad.c:398:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=] net/rxrpc/rxkad.c:242:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=]

This passes the initial SKCIPHER_REQUEST_ON_STACK allocation to the leaf functions for reuse. Two requests allocated on the stack are not needed when only one is used at a time.

Signed-off-by Kees Cook <[email protected]>

---
 net/rxrpc/rxkad.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

net/rxrpc/rxkad.c +13 ~~-12~~

index 278ac0807a60..6393391fac86 100644
@@ -146,10 +146,10 @@ static int rxkad_prime_packet_security(struct rxrpc_connection *conn)
 static int rxkad_secure_packet_auth(const struct rxrpc_call *call,
 				    struct sk_buff *skb,
 				    u32 data_size,
-				    void *sechdr)
+				    void *sechdr,
+				    struct skcipher_request *req)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxkad_level1_hdr hdr;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg;

@@ -183,12 +183,12 @@ static int rxkad_secure_packet_auth(const struct rxrpc_call *call,
 static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call,
 				       struct sk_buff *skb,
 				       u32 data_size,
-				       void *sechdr)
+				       void *sechdr,
+				       struct skcipher_request *req)
 {
 	const struct rxrpc_key_token *token;
 	struct rxkad_level2_hdr rxkhdr;
 	struct rxrpc_skb_priv *sp;
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[16];
 	struct sk_buff *trailer;

@@ -296,11 +296,12 @@ static int rxkad_secure_packet(struct rxrpc_call *call,
 		ret = 0;
 		break;
 	case RXRPC_SECURITY_AUTH:
-		ret = rxkad_secure_packet_auth(call, skb, data_size, sechdr);
+		ret = rxkad_secure_packet_auth(call, skb, data_size, sechdr,
+					       req);
 		break;
 	case RXRPC_SECURITY_ENCRYPT:
 		ret = rxkad_secure_packet_encrypt(call, skb, data_size,
-						  sechdr);
+						  sechdr, req);
 		break;
 	default:
 		ret = -EPERM;

@@ -316,10 +317,10 @@ static int rxkad_secure_packet(struct rxrpc_call *call,
  */
 static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 				 unsigned int offset, unsigned int len,
-				 rxrpc_seq_t seq)
+				 rxrpc_seq_t seq,
+				 struct skcipher_request *req)
 {
 	struct rxkad_level1_hdr sechdr;
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[16];
 	struct sk_buff *trailer;

@@ -402,11 +403,11 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
  */
 static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 				 unsigned int offset, unsigned int len,
-				 rxrpc_seq_t seq)
+				 rxrpc_seq_t seq,
+				 struct skcipher_request *req)
 {
 	const struct rxrpc_key_token *token;
 	struct rxkad_level2_hdr sechdr;
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxrpc_crypt iv;
 	struct scatterlist _sg[4], *sg;
 	struct sk_buff *trailer;

@@ -549,9 +550,9 @@ static int rxkad_verify_packet(struct rxrpc_call *call, struct sk_buff *skb,
 	case RXRPC_SECURITY_PLAIN:
 		return 0;
 	case RXRPC_SECURITY_AUTH:
-		return rxkad_verify_packet_1(call, skb, offset, len, seq);
+		return rxkad_verify_packet_1(call, skb, offset, len, seq, req);
 	case RXRPC_SECURITY_ENCRYPT:
-		return rxkad_verify_packet_2(call, skb, offset, len, seq);
+		return rxkad_verify_packet_2(call, skb, offset, len, seq, req);
 	default:
 		return -ENOANO;
 	}

Signature · 6 lines

2.17.1


-- 
Kees Cook
Pixel Security

Arnd Bergmann

Acked-by on v1 1/1

2018-07-16 10:17 UTC #1 lore raw

Quoted 11 lines · Kees Cook

The use of SKCIPHER_REQUEST_ON_STACK() will trigger FRAME_WARN warnings (when less than 2048) once the VLA is no longer hidden from the check:
net/rxrpc/rxkad.c:398:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=] net/rxrpc/rxkad.c:242:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=]
This passes the initial SKCIPHER_REQUEST_ON_STACK allocation to the leaf functions for reuse. Two requests allocated on the stack are not needed when only one is used at a time.
Signed-off-by Kees Cook <[email protected]>

This looks like a very nice solution to the problem.

Acked-by Arnd Bergmann <[email protected]>

Since the large stack usage could already cause problems in older kernels, should this be backported to stable kernels as well?

Arnd

Kees Cook

author

2018-07-19 04:29 UTC #2 lore raw

Quoted 11 lines · Arnd Bergmann

Quoted 10 lines · Kees Cook
The use of SKCIPHER_REQUEST_ON_STACK() will trigger FRAME_WARN warnings (when less than 2048) once the VLA is no longer hidden from the check:
net/rxrpc/rxkad.c:398:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=] net/rxrpc/rxkad.c:242:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=]
This passes the initial SKCIPHER_REQUEST_ON_STACK allocation to the leaf functions for reuse. Two requests allocated on the stack are not needed when only one is used at a time.

Quoted 8 lines

Quoted 1 line
Signed-off-by Kees Cook <[email protected]>
This looks like a very nice solution to the problem.
Acked-by Arnd Bergmann <[email protected]>
Since the large stack usage could already cause problems in older kernels, should this be backported to stable kernels as well?

I don't think this hits the bar for doing a -stable patch, but if you think I should, I can do it.

-Kees

Signature · 2 lines

Kees Cook
Pixel Security

Eric Biggers

2018-07-16 17:42 UTC #3 lore raw

In reply to Kees Cook

Quoted 103 lines · Kees Cook

The use of SKCIPHER_REQUEST_ON_STACK() will trigger FRAME_WARN warnings (when less than 2048) once the VLA is no longer hidden from the check:

This passes the initial SKCIPHER_REQUEST_ON_STACK allocation to the leaf functions for reuse. Two requests allocated on the stack are not needed when only one is used at a time.

Signed-off-by Kees Cook <[email protected]>

---
 net/rxrpc/rxkad.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

net/rxrpc/rxkad.c +13 ~~-12~~

index 278ac0807a60..6393391fac86 100644
@@ -146,10 +146,10 @@ static int rxkad_prime_packet_security(struct rxrpc_connection *conn)
 static int rxkad_secure_packet_auth(const struct rxrpc_call *call,
 				    struct sk_buff *skb,
 				    u32 data_size,
-				    void *sechdr)
+				    void *sechdr,
+				    struct skcipher_request *req)
 {
 	struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxkad_level1_hdr hdr;
 	struct rxrpc_crypt iv;
 	struct scatterlist sg;

@@ -183,12 +183,12 @@ static int rxkad_secure_packet_auth(const struct rxrpc_call *call,
 static int rxkad_secure_packet_encrypt(const struct rxrpc_call *call,
 				       struct sk_buff *skb,
 				       u32 data_size,
-				       void *sechdr)
+				       void *sechdr,
+				       struct skcipher_request *req)
 {
 	const struct rxrpc_key_token *token;
 	struct rxkad_level2_hdr rxkhdr;
 	struct rxrpc_skb_priv *sp;
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[16];
 	struct sk_buff *trailer;

@@ -296,11 +296,12 @@ static int rxkad_secure_packet(struct rxrpc_call *call,
 		ret = 0;
 		break;
 	case RXRPC_SECURITY_AUTH:
-		ret = rxkad_secure_packet_auth(call, skb, data_size, sechdr);
+		ret = rxkad_secure_packet_auth(call, skb, data_size, sechdr,
+					       req);
 		break;
 	case RXRPC_SECURITY_ENCRYPT:
 		ret = rxkad_secure_packet_encrypt(call, skb, data_size,
-						  sechdr);
+						  sechdr, req);
 		break;
 	default:
 		ret = -EPERM;

@@ -316,10 +317,10 @@ static int rxkad_secure_packet(struct rxrpc_call *call,
  */
 static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
 				 unsigned int offset, unsigned int len,
-				 rxrpc_seq_t seq)
+				 rxrpc_seq_t seq,
+				 struct skcipher_request *req)
 {
 	struct rxkad_level1_hdr sechdr;
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxrpc_crypt iv;
 	struct scatterlist sg[16];
 	struct sk_buff *trailer;

@@ -402,11 +403,11 @@ static int rxkad_verify_packet_1(struct rxrpc_call *call, struct sk_buff *skb,
  */
 static int rxkad_verify_packet_2(struct rxrpc_call *call, struct sk_buff *skb,
 				 unsigned int offset, unsigned int len,
-				 rxrpc_seq_t seq)
+				 rxrpc_seq_t seq,
+				 struct skcipher_request *req)
 {
 	const struct rxrpc_key_token *token;
 	struct rxkad_level2_hdr sechdr;
-	SKCIPHER_REQUEST_ON_STACK(req, call->conn->cipher);
 	struct rxrpc_crypt iv;
 	struct scatterlist _sg[4], *sg;
 	struct sk_buff *trailer;

@@ -549,9 +550,9 @@ static int rxkad_verify_packet(struct rxrpc_call *call, struct sk_buff *skb,
 	case RXRPC_SECURITY_PLAIN:
 		return 0;
 	case RXRPC_SECURITY_AUTH:
-		return rxkad_verify_packet_1(call, skb, offset, len, seq);
+		return rxkad_verify_packet_1(call, skb, offset, len, seq, req);
 	case RXRPC_SECURITY_ENCRYPT:
-		return rxkad_verify_packet_2(call, skb, offset, len, seq);
+		return rxkad_verify_packet_2(call, skb, offset, len, seq, req);
 	default:
 		return -ENOANO;
 	}

Signature · 1 line

2.17.1

How about doing the 'skcipher_request_set_tfm(req, call->conn->cipher)' and 'skcipher_request_zero(req);' just once, in the top-level function rxkad_verify_packet(), instead of before/after every time the request is used?

- Eric

Kees Cook

author

2018-07-19 04:31 UTC #4 lore raw

Quoted 11 lines · Eric Biggers

Quoted 10 lines · Kees Cook
The use of SKCIPHER_REQUEST_ON_STACK() will trigger FRAME_WARN warnings (when less than 2048) once the VLA is no longer hidden from the check:
net/rxrpc/rxkad.c:398:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=] net/rxrpc/rxkad.c:242:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=]
This passes the initial SKCIPHER_REQUEST_ON_STACK allocation to the leaf functions for reuse. Two requests allocated on the stack are not needed when only one is used at a time.

Quoted 8 lines

Quoted 5 lines
Signed-off-by Kees Cook <[email protected]>
---
 net/rxrpc/rxkad.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)
[...]
How about doing the 'skcipher_request_set_tfm(req, call->conn->cipher)' and 'skcipher_request_zero(req);' just once, in the top-level function rxkad_verify_packet(), instead of before/after every time the request is used?

Hm. While that does sound reasonable, I like having it be operationally unchanged. And changing this makes the caller function a bit more weird. Right now it's doing direct returns, and we'd need to cover error paths, etc. Having the "zero" _right_ after the encrypt/decrypt seems more robust to me.

-Kees

Signature · 2 lines

Kees Cook
Pixel Security