Fix table indexing in dwarf_search_unwind_table
#308
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`table_len` is used as an index into `table`, assuming it represents the number of entries. However, it is defined as the number of entries multiplied by `sizeof(unw_word_t)`. This is accounted for in other places that use `table_len`, e.g. in `lookup`, which divides out the size of `unw_word_t`, but the indexing expression uses `table_len` directly. So when `table` has say 2 entries, we're actually looking at index 16 rather than 2 in the comparison. This can cause the conditional to erroneously evaluate to true, allowing the following line to segfault. This was observed with JIT compiled code from Julia with LLVM on FreeBSD. Co-Authored-By: Jameson Nash <vtjnash@gmail.com>
vtjnash
approved these changes
Nov 6, 2021
This was referenced Nov 6, 2021
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Awesome, thanks! Nice find. |
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table_lenis used as an index intotable, assuming it represents the number of entries. However, it is defined as the number of entries multiplied bysizeof(unw_word_t). This is accounted for in other places that usetable_len, e.g. inlookup, which divides out the size ofunw_word_t, but the indexing expression usestable_lendirectly. So whentablehas say 2 entries, we're actually looking at index 15 rather than 1 in the comparison. This can cause the conditional to erroneously evaluate to true, allowing the following line to segfault.This was observed with JIT compiled code from Julia with LLVM on FreeBSD. It manifested as JuliaLang/julia#41943. Unfortunately we weren't able to come up with a minimal reproducer, as it happened seemingly sporadically in the Julia tests.
cc @vtjnash