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Add security best practice sections (#14798)

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Ryo Onodera
2021-01-26 08:36:11 +09:00
committed by GitHub
parent 74c83e6854
commit 60611ae8a0
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docs/src/developing/programming-model/transactions.md
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@@ -171,6 +171,26 @@ that this method only supports fixed sized types. Token utilizes the
trait to encode/decode instruction data for both token instructions as well as
token account states.
### Multiple instructions in a single transaction
A transaction can contain instructions in any order. This means a malicious
user could craft transactions that may pose instructions in an order that the
program has not been protected against. Programs should be hardened to properly
and safely handle any possible instruction sequence.
One not so obvious example is account deinitialization. Some programs may
attempt to deinitialize an account by setting its lamports to zero, with the
assumption that the runtime will delete the account. This assumption may be
valid between transactions, but it is not between instructions or cross-program
invocations. To harden against this, the program should also explicitly zero out the
account's data.
An example of where this could be a problem is if a token program, upon
transferring the token out of an account, sets the account's lamports to zero,
assuming it will be deleted by the runtime. If the program does zero out the
account's data, a malicious user could trail this instruction with another that
transfers the tokens a second time.
## Signatures
Each transaction explicitly lists all account public keys referenced by the