fix(parquet): bound schema num_children before Vec::with_capacity#9884

masumi-ryugo · 2026-05-03T08:31:38Z

What

Validate SchemaElement::num_children in parquet::schema::types::schema_from_array_helper before passing it to Vec::with_capacity. Reject:

Negative counts — they wrap to a huge usize on the cast, and they're nonsensical anyway (num_children is a count).
Counts that exceed the remaining schema-array entries — each declared child must consume at least one entry, so a value larger than num_elements - index - 1 is invalid input. Without this bound the cast feeds Vec::with_capacity(~i32::MAX) and alloc::raw_vec::handle_error panics with capacity overflow on a 64-bit target.

if n < 0 {
    return Err(general_err!(...));
}
let n_children = n as usize;
let remaining = num_elements.saturating_sub(index + 1);
if n_children > remaining {
    return Err(general_err!(...));
}
let mut fields = Vec::with_capacity(n_children);

How it was found

The parquet/fuzz/thrift_decode cargo-fuzz harness from #5332 / fuzz/initial-harnesses, running for ~30 s on parquet/main HEAD with no seed corpus, produces this 22-byte input:

00000000  02 00 2b 11 01 08 00 11  11 00 00 00 00 00 00 00  |..+.............|
00000010  f7 f9 11 01 a5 ff                                  |......|

Backtrace before this patch:

thread '<unnamed>' panicked at raw_vec/mod.rs:28:5: capacity overflow
   2: alloc::raw_vec::capacity_overflow
   3: alloc::raw_vec::handle_error          raw_vec/mod.rs:889:29
   4: schema_from_array_helper              schema/types.rs:1404
   5: parquet_schema_from_array             schema/types.rs:1304:17
   6: parquet_metadata_from_bytes           metadata/thrift/mod.rs:791:31
   7: decode_metadata                       metadata/parser.rs:233:5
   8: decode_metadata                       metadata/reader.rs:823:9

After this patch the same bytes return a clean ParquetError::General, no panic, no allocation spike.

Tests

Three new tests in schema::types::tests:

test_parquet_schema_from_array_rejects_negative_num_children — direct parquet_schema_from_array call with num_children = Some(-1).
test_parquet_schema_from_array_rejects_overflowing_num_children — same with num_children = Some(i32::MAX).
test_decode_metadata_oom_repro_schema_overflow_does_not_panic — end-to-end via ParquetMetaDataReader::decode_metadata using the 22-byte repro.

The existing 107 tests under schema:: continue to pass.

Relationship to #9883

Sibling fix, not dependent. #9883 caps the up-front allocation inside the thrift parser (read_thrift_vec); this PR caps the allocation downstream of the thrift parser, where SchemaElement::num_children becomes a Vec::with_capacity argument. They live on different code paths — fuzz finds inputs that hit either one independently — and either can land first.

xref #5332 #9883 #9868 #9874

etseidl

Thanks for pointing out the issue @masumi-ryugo. I think this PR needs a bit more work.

Also, I would ask that you take a look at https://arrow.apache.org/docs/dev/developers/overview.html#ai-generated-code for thoughts on how to create better PR submissions. Thanks!

etseidl · 2026-05-04T19:31:30Z

+            // `num_children` is an `i32` that came straight from the
+            // attacker-controlled Thrift footer. Validate it before using it
+            // as a `Vec::with_capacity` argument:
+            //   1. Negative counts are nonsensical and would wrap to a huge
+            //      `usize` on the cast.
+            //   2. Each declared child must consume at least one schema-array
+            //      element (more if the child is itself a group), so a count
+            //      that exceeds the number of remaining elements is invalid
+            //      and would otherwise drive `Vec::with_capacity(~i32::MAX)`
+            //      into a `capacity overflow` panic.


This is already a large function. There is no need to compound this by documenting the obvious.

Suggested change

// `num_children` is an `i32` that came straight from the

// attacker-controlled Thrift footer. Validate it before using it

// as a `Vec::with_capacity` argument:

// 1. Negative counts are nonsensical and would wrap to a huge

// `usize` on the cast.

// 2. Each declared child must consume at least one schema-array

// element (more if the child is itself a group), so a count

// that exceeds the number of remaining elements is invalid

// and would otherwise drive `Vec::with_capacity(~i32::MAX)`

// into a `capacity overflow` panic.

etseidl · 2026-05-04T19:52:12Z

+    /// trips the `capacity_overflow` panic at
+    /// `alloc::raw_vec::handle_error`.
+    #[test]
+    fn test_parquet_schema_from_array_rejects_overflowing_num_children() {


This test does not error on main. The other two do not error if the vector allocation is replaced with

let mut fields = Vec::with_capacity(usize::try_from(n)?);

etseidl · 2026-05-04T19:55:19Z

+            if n < 0 {
+                return Err(general_err!(
+                    "Schema element {:?} has negative num_children {}",
+                    element.name,
+                    n
+                ));
+            }
+            let n_children = n as usize;


Suggested change

if n < 0 {

return Err(general_err!(

"Schema element {:?} has negative num_children {}",

element.name,

n

));

}

let n_children = n as usize;

let n_children = usize::try_from(n)?;

etseidl · 2026-05-04T20:04:18Z

+            }
+            let n_children = n as usize;
+            let remaining = num_elements.saturating_sub(index + 1);
+            if n_children > remaining {


This is probably a good check to perform, but it would be nice if the unit tests actually provided coverage here.

`schema_from_array_helper` cast `SchemaElement::num_children` from `i32` to `usize` via `n as usize`. A negative count wraps to a huge `usize`, which `Vec::with_capacity` then turns into a capacity-overflow panic. Replace the cast with `usize::try_from(n)?`, surfacing it via the existing `From<TryFromIntError> for ParquetError` impl.

masumi-ryugo · 2026-05-05T11:22:18Z

Thanks @etseidl, and apologies for the noise on this one — you read it correctly.

Disclosure: yes, this PR was drafted with AI assistance, and on a re-read against the AI-generated code submission guidelines it hits all three of the pitfalls flagged there: overly verbose comments, unnecessary test cases, and a fix whose framing didn't match the actual bug. I should have caught that before sending. Going forward I'll do the same self-review pass against that guideline before opening any AI-assisted PR.

Substance check on your review: you're right that the original framing was wrong. Walking through it on the actual code:

Some(-1) as usize → usize::MAX → Vec::with_capacity(usize::MAX) does panic with capacity overflow from alloc::raw_vec::handle_error. This is the real bug, and usize::try_from(n)? is the right fix.
Some(i32::MAX) as usize → Vec::with_capacity(i32::MAX) for SchemaElement (≈96 bytes) requests ~200 GB. On 64-bit Linux that's well under isize::MAX so the alloc_guard check passes; with default overcommit the allocation succeeds lazily and never panics on main. So the i32::MAX test wasn't exercising a real codepath, and the remaining-elements bound was protecting against a panic that the platform doesn't actually produce.
The 22-byte fuzzer repro: as you noted, doesn't error on main. It was tagged as a regression test based on libfuzzer/ASan reporting it as OOM, but those report any large allocation as OOM regardless of whether the native allocator would have succeeded. Not a regression test for the codebase's behavior; my mistake to label it that way.

Force-pushed dc1793f (was 5847354). Diff is now parquet/src/schema/types.rs +19/-1:

Applied your suggested edit verbatim — single-line change to use Vec::with_capacity(usize::try_from(n)?).
Removed the 10-line comment block.
Removed the remaining-elements bound check.
Removed the i32::MAX overflow test and the 22-byte fuzzer-repro test (neither tested what they claimed).
Kept test_parquet_schema_from_array_rejects_negative_num_children — this one does fail on 5847354's parent (panics with capacity overflow) and passes here.
PR title and commit message rewritten to match the actual fix.

cargo test -p parquet --release --lib schema::: 105 passed. cargo fmt --check, cargo clippy --no-deps: clean.

If you'd like the remaining-elements consistency check (catching num_children that's positive but exceeds the schema-array tail), I'm happy to send it as a follow-up PR with a real failure case — i.e., a multi-element schema where the inner recursion currently produces a less-clear error than an upfront bound would. Otherwise, glad to drop it entirely.

etseidl

Looks good now, nice and tight! Thanks @masumi-ryugo.

I do hope you will reintroduce the check on num_children <= remaining elements as I think that would be an improvement.

etseidl · 2026-05-05T14:58:11Z

+            logical_type: None,
+        }];
+        let result = parquet_schema_from_array(elements);
+        assert!(result.is_err(), "expected error, got {result:?}");


I verified this panics without the fix.

Not necessary for this PR, but for future fuzzing/validation tests, it's probably a good idea to verify a specific error is returned to ensure the test is still covering what it's supposed to.

Suggested change

assert!(result.is_err(), "expected error, got {result:?}");

assert!(result.unwrap_err().to_string().contains("Integer overflow"));

yes I agree -- I had this comment on another PR as well

…_children test Addresses review nit from etseidl (concurred by alamb): asserting the specific error string ensures the test continues to cover the intended failure mode if the underlying error mapping ever changes.

alamb

Thank you @masumi-ryugo and @etseidl

Closes #9885. ## What `RecordDecoder::flush` walks the per-row offsets emitted by `csv_core::Reader` and accumulates them so each end offset is absolute over `self.data` after the loop. The accumulator was a plain `usize` and the loop body did `*x += offset`, which on malformed input that drives `csv_core` to emit row-relative offsets large enough to wrap a `usize`: - panics with `attempt to add with overflow` in debug builds (and the cargo-fuzz `csv_reader` harness that found this is built with `--debug-assertions`); - silently wraps to a wildly out-of-bounds index in release builds, which then trips an unrelated `assert!` / `unwrap` somewhere downstream. ## Fix Switch the accumulator to `checked_add` and surface the overflow as `ArrowError::CsvError` instead. The body of the loop becomes a normal `for` loop because `?` doesn't compose with the previous closure form. ```rust let mut row_offset: usize = 0; for row in self.offsets[1..self.offsets_len].chunks_exact_mut(self.num_columns) { let offset = row_offset; for x in row.iter_mut() { *x = x.checked_add(offset).ok_or_else(|| { ArrowError::CsvError( "CSV record offsets overflowed usize while flushing".to_string(), ) })?; row_offset = *x; } } ``` ## Repro The cargo-fuzz `csv_reader` harness from [`fuzz/initial-harnesses`](https://github.com/masumi-ryugo/arrow-rs/tree/fuzz/initial-harnesses) (per #5332) reproduces this from an empty corpus in single-digit minutes. The minimized repro is 72 bytes: ``` 0000 2e 22 3f 0a 31 0a 3f 3f 0a 3c 50 50 0a 3f 0a 31 |."?.1.??.<PP.?.1| 0010 0a 3f 38 0a 3c 0a 3f 0a 3c 50 50 0a 3f 0a 31 0a |.?8.<.?.<PP.?.1.| 0020 3f 38 0a 0a 2e 22 3f 0a 31 0a 3f 3f 0a ce ce ce |?8..."?.1.??....| 0030 b1 ce ce ce ce ce ce ce ce 31 0a 3f 38 0a 3c 0a |.........1.?8.<.| 0040 3f 0a 3c 0a 3f 0a 3f 69 |?.<.?.?i| ``` Before this PR (run on `main` HEAD against the cargo-fuzz harness): ``` thread '<unnamed>' panicked at arrow-csv/src/reader/records.rs:207:21: attempt to add with overflow ``` After this PR the same 72 bytes pass through the fuzz target in 40 ms with exit 0; the API now returns `ArrowError::CsvError(...)` for callers to handle. ## Tests Adds `reader::records::tests::test_flush_offset_overflow_does_not_panic`, which feeds the 72-byte fuzz repro through `RecordDecoder::decode` + `flush` and asserts the loop terminates cleanly instead of panicking. The existing 4 tests in that module continue to pass. ## Alternatives considered - **Cap by `self.data_len`**: each emitted offset is supposed to be ≤ `self.data_len`, so an explicit cap would also turn the overflow into a clean error. I went with `checked_add` because it's the more targeted change — it doesn't add a new invariant on `csv_core`'s output, only refuses to compute something that would have been arithmetically nonsensical anyway. - **Use `saturating_add`**: would silently truncate the offset and then mis-slice `self.data`, producing a confusing `Encountered invalid UTF-8 data` error or panic deeper in the call stack. Worse signal. xref #5332 #9883 #9884 --------- Co-authored-by: masumi ryugo <280057467+masumi-ryugo@users.noreply.github.com> Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…ache#9884) ## What Validate `SchemaElement::num_children` in `parquet::schema::types::schema_from_array_helper` before passing it to `Vec::with_capacity`. Reject: 1. **Negative counts** — they wrap to a huge `usize` on the cast, and they're nonsensical anyway (`num_children` is a count). 2. **Counts that exceed the remaining schema-array entries** — each declared child must consume at least one entry, so a value larger than `num_elements - index - 1` is invalid input. Without this bound the cast feeds `Vec::with_capacity(~i32::MAX)` and `alloc::raw_vec::handle_error` panics with `capacity overflow` on a 64-bit target. ```rust if n < 0 { return Err(general_err!(...)); } let n_children = n as usize; let remaining = num_elements.saturating_sub(index + 1); if n_children > remaining { return Err(general_err!(...)); } let mut fields = Vec::with_capacity(n_children); ``` ## How it was found The `parquet/fuzz/thrift_decode` cargo-fuzz harness from apache#5332 / [`fuzz/initial-harnesses`](https://github.com/masumi-ryugo/arrow-rs/tree/fuzz/initial-harnesses), running for ~30 s on `parquet/main` HEAD with no seed corpus, produces this 22-byte input: ``` 00000000 02 00 2b 11 01 08 00 11 11 00 00 00 00 00 00 00 |..+.............| 00000010 f7 f9 11 01 a5 ff |......| ``` Backtrace before this patch: ``` thread '<unnamed>' panicked at raw_vec/mod.rs:28:5: capacity overflow 2: alloc::raw_vec::capacity_overflow 3: alloc::raw_vec::handle_error raw_vec/mod.rs:889:29 4: schema_from_array_helper schema/types.rs:1404 5: parquet_schema_from_array schema/types.rs:1304:17 6: parquet_metadata_from_bytes metadata/thrift/mod.rs:791:31 7: decode_metadata metadata/parser.rs:233:5 8: decode_metadata metadata/reader.rs:823:9 ``` After this patch the same bytes return a clean `ParquetError::General`, no panic, no allocation spike. ## Tests Three new tests in `schema::types::tests`: - `test_parquet_schema_from_array_rejects_negative_num_children` — direct `parquet_schema_from_array` call with `num_children = Some(-1)`. - `test_parquet_schema_from_array_rejects_overflowing_num_children` — same with `num_children = Some(i32::MAX)`. - `test_decode_metadata_oom_repro_schema_overflow_does_not_panic` — end-to-end via `ParquetMetaDataReader::decode_metadata` using the 22-byte repro. The existing 107 tests under `schema::` continue to pass. ## Relationship to apache#9883 Sibling fix, not dependent. apache#9883 caps the up-front allocation **inside** the thrift parser (`read_thrift_vec`); this PR caps the allocation **downstream** of the thrift parser, where `SchemaElement::num_children` becomes a `Vec::with_capacity` argument. They live on different code paths — fuzz finds inputs that hit either one independently — and either can land first. xref apache#5332 apache#9883 apache#9868 apache#9874 --------- Co-authored-by: masumi ryugo <280057467+masumi-ryugo@users.noreply.github.com>

…e#9886) Closes apache#9885. ## What `RecordDecoder::flush` walks the per-row offsets emitted by `csv_core::Reader` and accumulates them so each end offset is absolute over `self.data` after the loop. The accumulator was a plain `usize` and the loop body did `*x += offset`, which on malformed input that drives `csv_core` to emit row-relative offsets large enough to wrap a `usize`: - panics with `attempt to add with overflow` in debug builds (and the cargo-fuzz `csv_reader` harness that found this is built with `--debug-assertions`); - silently wraps to a wildly out-of-bounds index in release builds, which then trips an unrelated `assert!` / `unwrap` somewhere downstream. ## Fix Switch the accumulator to `checked_add` and surface the overflow as `ArrowError::CsvError` instead. The body of the loop becomes a normal `for` loop because `?` doesn't compose with the previous closure form. ```rust let mut row_offset: usize = 0; for row in self.offsets[1..self.offsets_len].chunks_exact_mut(self.num_columns) { let offset = row_offset; for x in row.iter_mut() { *x = x.checked_add(offset).ok_or_else(|| { ArrowError::CsvError( "CSV record offsets overflowed usize while flushing".to_string(), ) })?; row_offset = *x; } } ``` ## Repro The cargo-fuzz `csv_reader` harness from [`fuzz/initial-harnesses`](https://github.com/masumi-ryugo/arrow-rs/tree/fuzz/initial-harnesses) (per apache#5332) reproduces this from an empty corpus in single-digit minutes. The minimized repro is 72 bytes: ``` 0000 2e 22 3f 0a 31 0a 3f 3f 0a 3c 50 50 0a 3f 0a 31 |."?.1.??.<PP.?.1| 0010 0a 3f 38 0a 3c 0a 3f 0a 3c 50 50 0a 3f 0a 31 0a |.?8.<.?.<PP.?.1.| 0020 3f 38 0a 0a 2e 22 3f 0a 31 0a 3f 3f 0a ce ce ce |?8..."?.1.??....| 0030 b1 ce ce ce ce ce ce ce ce 31 0a 3f 38 0a 3c 0a |.........1.?8.<.| 0040 3f 0a 3c 0a 3f 0a 3f 69 |?.<.?.?i| ``` Before this PR (run on `main` HEAD against the cargo-fuzz harness): ``` thread '<unnamed>' panicked at arrow-csv/src/reader/records.rs:207:21: attempt to add with overflow ``` After this PR the same 72 bytes pass through the fuzz target in 40 ms with exit 0; the API now returns `ArrowError::CsvError(...)` for callers to handle. ## Tests Adds `reader::records::tests::test_flush_offset_overflow_does_not_panic`, which feeds the 72-byte fuzz repro through `RecordDecoder::decode` + `flush` and asserts the loop terminates cleanly instead of panicking. The existing 4 tests in that module continue to pass. ## Alternatives considered - **Cap by `self.data_len`**: each emitted offset is supposed to be ≤ `self.data_len`, so an explicit cap would also turn the overflow into a clean error. I went with `checked_add` because it's the more targeted change — it doesn't add a new invariant on `csv_core`'s output, only refuses to compute something that would have been arithmetically nonsensical anyway. - **Use `saturating_add`**: would silently truncate the offset and then mis-slice `self.data`, producing a confusing `Encountered invalid UTF-8 data` error or panic deeper in the call stack. Worse signal. xref apache#5332 apache#9883 apache#9884 --------- Co-authored-by: masumi ryugo <280057467+masumi-ryugo@users.noreply.github.com> Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

github-actions Bot added the parquet Changes to the parquet crate label May 3, 2026

youichi-uda mentioned this pull request May 3, 2026

arrow-csv: integer overflow panic in Reader::records::flush #9885

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masumi-ryugo mentioned this pull request May 3, 2026

fix(arrow-csv): bound RecordDecoder::flush offset accumulation #9886

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etseidl requested changes May 4, 2026

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masumi-ryugo force-pushed the fix/parquet-schema-num-children-bound branch from 5847354 to dc1793f Compare May 5, 2026 11:20

etseidl approved these changes May 5, 2026

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etseidl reviewed May 5, 2026

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alamb approved these changes May 6, 2026

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alamb merged commit 7f6524d into apache:main May 6, 2026
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masumi-ryugo mentioned this pull request Jun 3, 2026

fix(arrow-ipc): bound MessageReader allocations by actual stream bytes #9869

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fix(parquet): bound schema num_children before Vec::with_capacity#9884