[3.4] Fix use-after-free when resizing exivars #13637
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[Bug #21438] Previously GC could trigger a table rebuild of the generic ivar st_table in the middle of calling the st_update callback. This could cause entries to be reallocated or rearranged and the update to be for the wrong entry. This commit adds an assertion to make that case easier to detect, and replaces the st_update with a separate st_lookup and st_insert. Also free after insert in generic_ivar_set_shape_ivptr Previously we were performing a realloc and then inserting the new value into the table. If the table was flagged as requiring a rebuild, this could trigger GC work and marking within that GC could access the ivptr freed by realloc. Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org> Co-authored-by: Jean Boussier <byroot@ruby-lang.org>
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k0kubun
approved these changes
Jun 18, 2025
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[Bug #21438]
Ref: https://bugs.ruby-lang.org/issues/21438
Backport of #13635 and #13589.
Previously GC could trigger a table rebuild of the generic ivar st_table in the middle of calling the st_update callback.
This could cause entries to be reallocated or rearranged and the update to be for the wrong entry.
This commit adds an assertion to make that case easier to detect, and replaces the st_update with a separate st_lookup and st_insert.
Also free after insert in generic_ivar_set_shape_ivptr
Previously we were performing a realloc and then inserting the new value into the table.
If the table was flagged as requiring a rebuild, this could trigger GC work and marking within that GC could access the ivptr freed by realloc.