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[Bug #21357] Fix crash in Hash#merge with block

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Prior to 49b306ecb9
the `optional_arg` passed from `rb_hash_update_block_i` to `tbl_update`
was a hash value (i.e. a VALUE). After that commit it changed to an
`update_call_args`.

If the block sets or changes the value, `tbl_update_modify` will set the
`arg.value` back to an actual value and we won't crash. But in the case
where the block returns the original value we end up calling
`RB_OBJ_WRITTEN` with the `update_call_args` which is not expected and
may crash.

`arg.value` appears to only be used to pass to `RB_OBJ_WRITTEN` (others
who need the `update_call_args` get it from `arg.arg`), so I don't think
it needs to be set to anything upfront. And `tbl_update_modify` will set
the `arg.value` in the cases we need the write barrier.
This commit is contained in:
Daniel Colson 2025-05-21 22:00:12 -04:00 • committed by Yusuke Endoh
parent 7154b4208b
commit 0564973196
Notes: git 2025-05-22 03:26:07 +00:00
2 changed files with 7 additions and 2 deletions
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4
hash.c
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@ -1723,14 +1723,14 @@ tbl_update(VALUE hash, VALUE key, tbl_update_func func, st_data_t optional_arg)
.func = func,
.hash = hash,
.key = key,
.value = (VALUE)optional_arg,
.value = 0
};
int ret = rb_hash_stlike_update(hash, key, tbl_update_modify, (st_data_t)&arg);
/* write barrier */
RB_OBJ_WRITTEN(hash, Qundef, arg.key);
RB_OBJ_WRITTEN(hash, Qundef, arg.value);
if (arg.value) RB_OBJ_WRITTEN(hash, Qundef, arg.value);
return ret;
}