Using strncmp instead of strcmp to make the function robust and safe from buffer overruns. #33449
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PR #33449: Size comparison from 878fbb7 to d9cc3e8 Increases (3 builds for linux)
Decreases (3 builds for efr32, linux)
Full report (81 builds for bl602, bl702, bl702l, cc13x4_26x4, cc32xx, cyw30739, efr32, esp32, linux, mbed, nrfconnect, nxp, psoc6, qpg, stm32, telink)
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jmartinez-silabs
approved these changes
May 14, 2024
kiel-apple
approved these changes
May 14, 2024
| @@ -171,7 +171,7 @@ bool HandleNullableOptional(Argument & arg, char * argValue, std::function<bool( | |||
| if (arg.isNullable()) | |||
| { | |||
| auto * nullable = reinterpret_cast<chip::app::DataModel::Nullable<T> *>(arg.value); | |||
| if (strcmp(argValue, "null") == 0) | |||
| if (argValue != nullptr && strncmp(argValue, "null", 4) == 0) | |||
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How can argValue be not null-terminated? So how do we then know the size of it?
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Yes, it is impossible in this case, we use strncmp for argument comparisons in other cases, but in one instance, we use strcmp(argValue, "null").
strncmp would only be necessary if argValue was not null-terminated and had a length of exactly 4, making strcmp unsafe. However, since argValue is always null-terminated in this context, it is safe to use either strncmp(argValue, "null", 4) or strcmp(argValue, "null").
This change is intended to standardize the method used for argument comparison in the code.
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Just to follow up on the Slack thread about this: "standardizing" breaks the code. The places that use strncmp are doing prefix checks, but this one is supposed to be an equality check. We don't want to treat all strings starting with "null" as the null value.
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We use strncmp throughout examples/chip-tool/commands/common/Command.cpp for argument comparisons, but in one instance, we use strcmp(argValue, "null").
strncmp would only be necessary if argValue was not null-terminated and had a length of exactly 4, making strcmp unsafe. However, since argValue is always null-terminated in this context, it is safe to use either strncmp(argValue, "null", 4) or strcmp(argValue, "null").
This change is intended to standardize the method used for argument comparison in the code.