Reject tar sparse blocks larger than the entry size#780
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garydgregory
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Jul 5, 2026
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Hello @kali834x
Thank you for the PR. Please see my comments.
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| private static void appendPadded(final ByteArrayOutputStream out, final byte[] data) { | ||
| out.write(data, 0, data.length); | ||
| final int rem = data.length % 512; |
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Define or reuse a constant for the magic number 512.
| } | ||
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| private static byte[] ustarHeader(final String name, final long size, final char typeFlag) { | ||
| final byte[] header = new byte[512]; |
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Define or reuse a constant for the magic number 512.
| final byte[] payload = "the following entry".getBytes(java.nio.charset.StandardCharsets.US_ASCII); | ||
| appendPadded(bos, ustarHeader("next.bin", payload.length, '0')); | ||
| appendPadded(bos, payload); | ||
| bos.write(new byte[1024], 0, 1024); // two zero EOF records |
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Define or reuse a constant for the magic number 1024. Is it a coincidence that this test uses this number which is 512 *2, another magic number in the test?
| // A second entry follows, whose bytes must not be reachable through the sparse entry. | ||
| private byte[] sparseArchiveWithNumbytesLargerThanSize() { | ||
| final ByteArrayOutputStream bos = new ByteArrayOutputStream(); | ||
| final String pax = paxRecord("GNU.sparse.size", "1048576") + paxRecord("GNU.sparse.map", "0,1048576"); |
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Is 1048576 used both on this line meant to be exactly the same? If so, refactor.
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buildSparseInputStreams in TarArchiveInputStream and TarFile size the non-hole sub-streams from each sparse header's numbytes, and the only geometry guard, getOrderedSparseHeaders, bounds offset+numbytes against the logical realSize rather than the entry's stored size. a crafted gnu/pax sparse entry can set a small header size but a sparse map whose numbytes sum is much larger (realsize == numbytes so the existing realSize check passes), and reading that entry then pulls bytes belonging to the following entries. this accumulates the physical block bytes while building the streams and fails with an ArchiveException once they exceed currEntry.getSize(). the sum equals the entry size for every valid sparse variant (old gnu, pax 0.x, star), with slack only for the pax 1.x in-data map, so no valid archive is rejected. the added SparseFilesTest case reads a 4-byte entry whose map claims a 1 MiB block and now throws for both readers instead of over-reading into the next entry.
mvn; that'smvnon the command line by itself.