tar: Keep block alignment after pax error #2637
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If a pax attribute has a 0 length value and no newline, the tar reader gets out of sync with block alignment. This happens because the pax parser assumes that variable value_length (which includes the terminating newline) is at least 1. To get the real value length, 1 is subtracted. This result is subtracted from extsize, which in this case would lead to `extsize -= -1`, i.e. the remaining byte count is increased. Such an unexpected calculation leads to an off-by-one when skipping to the next block. In supplied test case, bsdtar complains that the checksum of the next block is wrong. Since the tar parser was not properly 512 bytes aligned, this is no surprise. Gracefully handle such a case like GNU tar does and warn the user that an invalid attribute has been encountered. Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
kientzle
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May 25, 2025
mmatuska
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May 31, 2025
tar: Keep block alignment after pax error (cherry picked from commit 341dd5d)
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If a pax attribute has a 0 length value and no newline, the tar reader gets out of sync with block alignment.
This happens because the pax parser assumes that variable value_length (which includes the terminating newline) is at least 1. To get the real value length, 1 is subtracted. This result is subtracted from extsize, which in this case would lead to
extsize -= -1, i.e. the remaining byte count is increased.Such an unexpected calculation leads to an off-by-one when skipping to the next block. In supplied test case, bsdtar complains that the checksum of the next block is wrong. Since the tar parser was not properly 512 bytes aligned, this is no surprise.
Gracefully handle such a case like GNU tar does and warn the user that an invalid attribute has been encountered.