Custom Data: make get_layer_index_n always safely handle n overrun. #110812

Alexander Gavrilov · 2023-08-04T19:57:10+02:00

2023-08-04 19:57:10 +02:00

This function is used to retrieve the index of the n'th layer of
the specified type, if it exists. Currently the way it handles
an n value that is too big is inconsistent: if there are more
layers of different types following the ones of the correct type,
and n isn't too big, it will safely detect that the corresponding
layer is of a different type and return -1. However, if the value
results in a buffer overrun, it causes an assertion or crash.

This means that safe code should currently ensure n is always
correct, making the type check in this function pointless.
Moreover, checking the range in the caller may incur more
overhead than making this code safe.

This changes the assert into a check to ensure consistent behavior.

This function is used to retrieve the index of the n'th layer of the specified type, if it exists. Currently the way it handles an n value that is too big is inconsistent: if there are more layers of different types following the ones of the correct type, and n isn't too big, it will safely detect that the corresponding layer is of a different type and return -1. However, if the value results in a buffer overrun, it causes an assertion or crash. This means that safe code should currently ensure n is always correct, making the type check in this function pointless. Moreover, checking the range in the caller may incur more overhead than making this code safe. This changes the assert into a check to ensure consistent behavior.

Alexander Gavrilov added 1 commit 2023-08-04 19:57:21 +02:00

74090f1cbd Custom Data: make get_layer_index_n always safely handle n overrun.

This function is used to retrieve the index of the n'th layer of
the specified type, if it exists. Currently the way it handles
an n value that is too big is inconsistent: if there are more
layers of different types following the ones of the correct type,
and n isn't too big, it will safely detect that the corresponding
layer is of a different type and return -1. However, if the value
results in a buffer overrun, it causes an assertion or crash.

This means that safe code should currently ensure n is always
correct, making the type check in this function pointless.
Moreover, checking the range in the caller may incur more
overhead than making this code safe.

This changes the assert into a check to ensure consistent behavior.

Hans Goudey approved these changes 2023-08-04 20:00:18 +02:00

Alexander Gavrilov merged commit 9921c3532c into main

2023-08-04 20:40:11 +02:00

Alexander Gavrilov referenced this issue from a commit

2023-08-04 20:40:11 +02:00

Custom Data: make get_layer_index_n always safely handle n overrun.

Alexander Gavrilov deleted branch pr-customdata-layer-index

2023-08-04 20:40:13 +02:00

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Custom Data: make get_layer_index_n always safely handle n overrun. #110812