[PATCH] D43819: [ELF] - Restrict section offsets that exceeds file size.

[James Henderson via Phabricator via llvm-commits]

jhenderson added a comment.

In https://reviews.llvm.org/D43819#1025064, @grimar wrote:

> I am not sure I understand the use case, sorry. We normally can not have an empty section at the end of the file, because we place section header table there.
>  If somehow section offset is damaged during calculation because of overflows, then `((Sec->Offset >= FileSize) || (Sec->Offset + Sec->Size >= FileSize)` check will catch it and report an error to prevent
>  mapped buffer overflow and crash during writing. That is what this code supposed to do. What am I missing?


It's a correctness thing again. Ultimately, you are correct, we //currently// can't generate sections at the end of the file, because the section header table is written there. However, this may not always be the case, and then we'd have a bug. Two potential future use cases might be a) writing the section header table earlier in the file (although admittedly I don't know why we would, but it is valid), or b) not writing the section header table at all (since linked ELFs don't require section headers in order to be run).
Sec->Offset == FileSize (or Sec->Offset + Sec->Size == FileSize - note that this latter case actually applies to non-empty sections too).

We don't need to add any additional code to get this. Simply change the '>=' to '>' in the comparisons.


https://reviews.llvm.org/D43819