The output buffer passed to qq_encrypt needs to be 17 bytes bigger

than the data you're encrypting, not 16 bytes bigger.  Fixes #10191.
It's hard to say whether this actually causes problems.  My guess is
that it does not.

However, the way the qq protocol plugin constructs the plain text
buffer to be passed to qq_encrypt is error prone, and the many calls
to g_newa(guint8, MAX_PACKET_SIZE) are really bad because
MAX_PACKET_SIZE is 64KB.  This is a ridiculous amount of space to
request on the stack.  All these qq_put8 qq_put16 qq_put32 qq_putdata
functions should be changed to insert data into a dynamically
allocated GString instead of the stack-allocated buffers that they
use now.  This eliminates the potential for accidentally overwriting
the end of the buffer.

And the second g_newa() for the output buffer passed into qq_encrypt()
should be changed to allocate space on the heap in most places because,
as previously noted, 64KB is a ridiculous amount of memory to request
from the stack.

Heap allocation may be expensive when compared to stack allocation, but
I feel it's usually worth it to eliminate the possibilty of buffer
overflow.

4 files changed, 35 insertions, 30 deletions

diff --git a/libpurple/protocols/qq/file_trans.c b/libpurple/protocols/qq/file_trans.c
index bbcdb8da68..3f078fc9b6 100644
--- a/libpurple/protocols/qq/file_trans.c
+++ b/libpurple/protocols/qq/file_trans.c
@@ -334,7 +334,7 @@ void qq_send_file_ctl_packet(PurpleConnection *gc, guint16 packet_type, guint32
 		raw_data, bytes,
 		"sending packet[%s]:", qq_get_file_cmd_desc(packet_type));
 
-	encrypted = g_newa(guint8, bytes + 16);
+	encrypted = g_newa(guint8, bytes + 17);
 	encrypted_len = qq_encrypt(encrypted, raw_data, bytes, info->file_session_key);
 	/*debug: try to decrypt it */
 
diff --git a/libpurple/protocols/qq/qq_base.c b/libpurple/protocols/qq/qq_base.c
index 511a98e6a3..969e698fe2 100644
--- a/libpurple/protocols/qq/qq_base.c
+++ b/libpurple/protocols/qq/qq_base.c
@@ -245,10 +245,10 @@ void qq_request_login(PurpleConnection *gc)
 
 	g_return_if_fail(qd->ld.token != NULL && qd->ld.token_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	bytes = 0;
 	/* now generate the encrypted data
@@ -609,7 +609,7 @@ void qq_request_get_server(PurpleConnection *gc)
 	raw_data = g_newa(guint8, 128);
 	memset(raw_data, 0, 128);
 
-	encrypted = g_newa(guint8, 128 + 16);	/* 16 bytes more */
+	encrypted = g_newa(guint8, 128 + 17);	/* 17 bytes more */
 
 	bytes = 0;
 	if (qd->redirect == NULL) {
@@ -682,10 +682,10 @@ void qq_request_token_ex(PurpleConnection *gc)
 
 	g_return_if_fail(qd->ld.token != NULL && qd->ld.token_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	bytes = 0;
 	bytes += qq_put8(raw_data + bytes, qd->ld.token_len);
@@ -721,10 +721,10 @@ void qq_request_token_ex_next(PurpleConnection *gc)
 
 	g_return_if_fail(qd->ld.token != NULL && qd->ld.token_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	bytes = 0;
 	bytes += qq_put8(raw_data + bytes, qd->ld.token_len);
@@ -765,10 +765,10 @@ static void request_token_ex_code(PurpleConnection *gc,
 	g_return_if_fail(qd->ld.token != NULL && qd->ld.token_len > 0);
 	g_return_if_fail(code != NULL && code_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	bytes = 0;
 	bytes += qq_put8(raw_data + bytes, qd->ld.token_len);
@@ -998,10 +998,10 @@ void qq_request_check_pwd(PurpleConnection *gc)
 
 	g_return_if_fail(qd->ld.token_ex != NULL && qd->ld.token_ex_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	/* Encrypted password and put in encrypted */
 	bytes = 0;
@@ -1166,10 +1166,10 @@ void qq_request_login_2007(PurpleConnection *gc)
 
 	g_return_if_fail(qd->ld.token != NULL && qd->ld.token_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	/* Encrypted password and put in encrypted */
 	bytes = 0;
@@ -1342,10 +1342,10 @@ void qq_request_login_2008(PurpleConnection *gc)
 
 	g_return_if_fail(qd->ld.token != NULL && qd->ld.token_len > 0);
 
-	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 16);
-	memset(raw_data, 0, MAX_PACKET_SIZE - 16);
+	raw_data = g_newa(guint8, MAX_PACKET_SIZE - 17);
+	memset(raw_data, 0, MAX_PACKET_SIZE - 17);
 
-	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 16 bytes more */
+	encrypted = g_newa(guint8, MAX_PACKET_SIZE);	/* 17 bytes more */
 
 	/* Encrypted password and put in encrypted */
 	bytes = 0;
diff --git a/libpurple/protocols/qq/qq_crypt.c b/libpurple/protocols/qq/qq_crypt.c
index aab83e14d6..07f1d2a869 100644
--- a/libpurple/protocols/qq/qq_crypt.c
+++ b/libpurple/protocols/qq/qq_crypt.c
@@ -171,7 +171,12 @@ static inline void encrypt_out(guint8 *crypted, const gint crypted_len, const gu
 	}
 }
 
-/* length of crypted buffer must be plain_len + 16*/
+/* length of crypted buffer must be plain_len + 17*/
+/*
+ * The above comment used to say "plain_len + 16", but based on the
+ * behavior of the function that is wrong.  If you give this function
+ * a plain string with len%8 = 7 then the returned length is len+17
+ */
 gint qq_encrypt(guint8* crypted, const guint8* const plain, const gint plain_len, const guint8* const key)
 {
 	guint8 *crypted_ptr = crypted;		/* current position of dest */
diff --git a/libpurple/protocols/qq/qq_network.c b/libpurple/protocols/qq/qq_network.c
index da3f033d45..2f638f9b4d 100644
--- a/libpurple/protocols/qq/qq_network.c
+++ b/libpurple/protocols/qq/qq_network.c
@@ -1146,8 +1146,8 @@ static gint send_cmd_detail(PurpleConnection *gc, guint16 cmd, guint16 seq,
 	qd = (qq_data *)gc->proto_data;
 	g_return_val_if_fail(data != NULL && data_len > 0, -1);
 
-	/* at most 16 bytes more */
-	encrypted = g_newa(guint8, data_len + 16);
+	/* at most 17 bytes more */
+	encrypted = g_newa(guint8, data_len + 17);
 	encrypted_len = qq_encrypt(encrypted, data, data_len, qd->session_key);
 	if (encrypted_len < 16) {
 		purple_debug_error("QQ_ENCRYPT", "Error len %d: [%05d] 0x%04X %s\n",
@@ -1223,8 +1223,8 @@ gint qq_send_server_reply(PurpleConnection *gc, guint16 cmd, guint16 seq, guint8
 		purple_debug_info("QQ", "<== [SRV-%05d] %s(0x%04X), datalen %d\n",
 				seq, qq_get_cmd_desc(cmd), cmd, data_len);
 #endif
-	/* at most 16 bytes more */
-	encrypted = g_newa(guint8, data_len + 16);
+	/* at most 17 bytes more */
+	encrypted = g_newa(guint8, data_len + 17);
 	encrypted_len = qq_encrypt(encrypted, data, data_len, qd->session_key);
 	if (encrypted_len < 16) {
 		purple_debug_error("QQ_ENCRYPT", "Error len %d: [%05d] 0x%04X %s\n",
@@ -1270,8 +1270,8 @@ static gint send_room_cmd(PurpleConnection *gc, guint8 room_cmd, guint32 room_id
 	seq = qd->send_seq;
 
 	/* Encrypt to encrypted with session_key */
-	/* at most 16 bytes more */
-	encrypted = g_newa(guint8, buf_len + 16);
+	/* at most 17 bytes more */
+	encrypted = g_newa(guint8, buf_len + 17);
 	encrypted_len = qq_encrypt(encrypted, buf, buf_len, qd->session_key);
 	if (encrypted_len < 16) {
 		purple_debug_error("QQ_ENCRYPT", "Error len %d: [%05d] %s (0x%02X)\n",