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Update contracts and descriptions

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This commit is contained in:
Denton Liu 2016-08-11 10:45:47 -04:00
parent 4737100d00
commit 058e5f0159
1 changed files with 13 additions and 4 deletions
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17
docs/common-patterns.rst
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@ -40,9 +40,9 @@ become the richest.
function becomeRichest() returns (bool) { function becomeRichest() returns (bool) {
if (msg.value > mostSent) { if (msg.value > mostSent) {
pending[richest] = msg.value;
richest = msg.sender; richest = msg.sender;
mostSent = msg.value; mostSent = msg.value;
pending[richest] = msg.value;
return true; return true;
} }
else { else {
@ -76,9 +76,14 @@ This is as opposed to the more intuitive sending pattern.
function becomeRichest() returns (bool) { function becomeRichest() returns (bool) {
if (msg.value > mostSent) { if (msg.value > mostSent) {
// Check if call succeeds to prevent an attacker
// from trapping the previous person's funds in
// this contract through a callstack attack
if (!richest.send(msg.value)) {
throw;
}
richest = msg.sender; richest = msg.sender;
mostSent = msg.value; mostSent = msg.value;
richest.send(msg.value);
return true; return true;
} }
else { else {
@ -88,8 +93,12 @@ This is as opposed to the more intuitive sending pattern.
} }
Notice that, in this example, an attacker could trap the Notice that, in this example, an attacker could trap the
previous richest person's funds in the contract by causing contract into an unusable state by causing the ``richest``
the execution of `send` to fail through a callstack attack. to be a contract that has a fallback function which consumes
more than the 2300 gas stipend. That way, whenever ``send``
is called to deliver funds to the "poisoned" contract, it
will cause execution to always fail because there is not
enough gas to finish the execution of the fallback function.
.. index:: access;restricting .. index:: access;restricting