variable.c: Fix generic_fields_lookup_ensure_size to avoid use-after-free
#13573
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
8e95c17 to
fd014ea
Compare
casperisfine
commented
Jun 10, 2025
…r-free The following diff can cause a use-after-free: ```c diff --git a/variable.c b/variable.c index a54bebc..53e01c1d60 100644 --- a/variable.c +++ b/variable.c @@ -1818,6 +1818,7 @@ generic_fields_lookup_ensure_size(st_data_t *k, st_data_t *v, st_data_t u, int e } fields_tbl = gen_fields_tbl_resize(fields_tbl, RSHAPE_CAPACITY(fields_lookup->shape_id)); + rb_gc_start(); *v = (st_data_t)fields_tbl; } ``` ```ruby (2..).step(-1) ``` Since `gen_fields_tbl_resize` uses `xrealloc`, we might trigger GC after the old buffer has been freed, but the pointer in the generic ivar table hasn't been updated yet. So if the `xrealloc` trigger GC, we'll mark a freed buffer.
fd014ea to
fb5bbc7
Compare
|
I think this bug is possible on 3.4.x |
|
Well, CI proves this wasn't the bug that cause the |
|
@peterzhu2118 tells me in |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The following diff can cause a use-after-free:
Since
gen_fields_tbl_resizeusesxrealloc, we might trigger GC after the old buffer has been freed, but the pointer in the generic ivar table hasn't been updated yet. So if thexrealloctrigger GC, we'll mark a freed buffer.