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Add funcs to avoid tricking user when using plugin

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Usually the length of an array is sent in a parameter.
Most of the times the developer simply uses U2BE/U4BE to get this length. It
is possible to forge a tx with a `length > sizeof(uint16_t/uint32_t)` and trick the
user into signing something different from what is shown.

For instance consider the following parameter:
00 ... 01 00 00 00 01

if the developer uses U2BE/U4BE, it is possible that this length is shown to the user
and if it is, the user will see the length as 1.
This commit is contained in:
Jorge Martins
2022-11-02 13:34:26 +01:00
parent 912c8afca6
commit ead85a0aaa
4 changed files with 35 additions and 1 deletions
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11
doc/ethapp_plugins.adoc
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@@ -134,6 +134,17 @@ The following return codes are expected, any other will abort the signing proces
* ETH_PLUGIN_RESULT_OK : if the plugin can be successfully initialized
* ETH_PLUGIN_RESULT_FALLBACK : if the signing logic should fallback to the generic one
There are already defined functions to extract data from a parameter:
[source,C]
----
void copy_address(uint8_t* dst, const uint8_t* parameter, uint8_t dst_size);
void copy_parameter(uint8_t* dst, const uint8_t* parameter, uint8_t dst_size);
// Get the value from the beginning of the parameter (right to left) and check if the rest of it is zero
bool U2BE_from_parameter(uint8_t* parameter, uint16_t* value);
bool U4BE_from_parameter(uint8_t* parameter, uint32_t* value);
----
### ETH_PLUGIN_FINALIZE
[source,C]