Fix B aux tag length check in cram_encode_aux #1725
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B tags need eight bytes: 2 for key 1 for type (B) 1 for sub-type 4 for count Previously this only checked for at least seven bytes, which could lead to a single byte out of bounds read. Credit to OSS-Fuzz Fixes oss-fuzz 65383
Ensure that large B aux item counts are caught in cram_encode_aux() so that the check to ensure that all the data is present works, and it can't attempt to make a block with negative length.
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B tags need eight bytes. Previously this only checked for at least seven, which could lead to a single byte out of bounds read. The impact of this is mostly limited by a later check on
blen; however it was also possible thatblencould overflow, allowing the check to incorrectly pass. A second commit expandsblenso it can't overflow, and ensures it has an acceptable value before passing it to the encode function.