Fix corruption that rarely occurs in 32-bit mode with wlog=25 #3361
Conversation
This file contains 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
|
A follow up is to add fuzzers that could catch this issue:
|
Cyan4973
reviewed
Dec 15, 2022
| @@ -6256,7 +6256,7 @@ ZSTD_compressSequences_internal(ZSTD_CCtx* cctx, | |||
|
|
|||
| if (!cctx->isFirstBlock && | |||
| ZSTD_maybeRLE(&cctx->seqStore) && | |||
| ZSTD_isRLE((BYTE const*)src, srcSize)) { | |||
| ZSTD_isRLE(ip, blockSize)) { | |||
Cyan4973
approved these changes
Dec 15, 2022
Fix an off-by-one error in the compressor that emits corrupt blocks if: * Zstd is compiled in 32-bit mode * The windowLog == 25 exactly * An offset of 2^25-3, 2^25-2, 2^25-1, or 2^25 is emitted * The bitstream had 7 bits leftover before writing the offset This bug has been present since before v1.0, but wasn't able to easily be triggered, since until somewhat recently zstd wasn't able to find matches that were within 128KB of the window size. Add a test case, and fix 2 bugs in `ZSTD_compressSequences()`: * The `ZSTD_isRLE()` check was incorrect. It wouldn't produce corruption, but it could waste CPU and not emit RLE even if the block was RLE * One windowSize was `1 << windowLog`, not `1u << windowLog` Thanks to @tansy for finding the issue, and giving us a reproducer! Fixes Issue facebook#3350.
daniellerozenblit
added a commit
to daniellerozenblit/oss-fuzz
that referenced
this pull request
Jan 20, 2023
We'd like to enable 32-bit mode fuzz tests for zstd for portability and to catch bugs such as this one (facebook/zstd#3361) that only occur when built in 32-bit mode. Is there anything else that needs to be done to enable 32-bit fuzzing for zstd?
daniellerozenblit
added a commit
to daniellerozenblit/oss-fuzz
that referenced
this pull request
Jan 24, 2023
We would like to extend zstd fuzzing to 32-bit in order to ensure the portability of zstd and find bugs (such as facebook/zstd#3361) that only occur on 32-bit platforms.
DavidKorczynski
pushed a commit
to google/oss-fuzz
that referenced
this pull request
Jan 25, 2023
We would like to extend zstd fuzzing to 32-bit in order to further ensure that zstd is portable and to find bugs (such as facebook/zstd#3361) that only occur on 32-bit platforms.
Merged
eamonnmcmanus
pushed a commit
to eamonnmcmanus/oss-fuzz
that referenced
this pull request
Mar 15, 2023
We would like to extend zstd fuzzing to 32-bit in order to further ensure that zstd is portable and to find bugs (such as facebook/zstd#3361) that only occur on 32-bit platforms.
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.
Fix an off-by-one error in the compressor that emits corrupt blocks if:
This bug has been present since before v1.0, but wasn't able to easily be triggered, since until somewhat recently zstd wasn't able to find matches that were within 128KB of the window size.
Add a test case, and fix 2 bugs in
ZSTD_compressSequences():ZSTD_isRLE()check was incorrect. It wouldn't produce corruption, but it could waste CPU and not emit RLE even if the block was RLE1 << windowLog, not1u << windowLogThanks to @tansy for finding the issue, and giving us a reproducer!
Fixes Issue #3350.