Seal failing on empty input file about kmyth HOT 5 CLOSED

I think we want to handle this both in the seal/unseal executable main functions, (early exit with a message if you hand it a size 0 file) and in the library seal/unseal library functions.

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Looking more closely at the code, I think by putting the check in kmyth_wrap_input in src/util/tpm2_kmyth_seal.c is the best place from the library perspective.

The src/seal/main.c executable should also check before doing all the TPM work.

from kmyth.

The first fix seems easy enough, but for the check in src/seal/main.c it looks like we would want to make a call to read_arbitrary_file() to get the data length. This is already done later on, in kmyth_wrap_input in src/util/tpm2_kmyth_seal.c. Doing this twice seems like it may be redundant if we are not passing along the output values.

from kmyth.

That's a good point. For now let's just fix kmyth_wrap_input. I still don't like the idea of doing all that TPM work just to find out the file has zero size, but it's going to be a bigger job to do the filesize check reasonably, so we can keep it in mind for future work if we decide it's worthwhile.

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I'm a bit late to the discussion but I figured this was relevant.

I'm adding error handling to read_arbitrary_file in src/util/tpm2_kmyth_io.c. A file size of 0 bytes may cause malloc to return NULL, which is indistinguishable from an allocation failure. Right now (with my edits) this returns 1, which would get caught and handled right before the fix added in #26, resurrecting the original issue.

I can change this so that read_arbitrary_file just short circuits and returns early when it encounters a 0 byte file, so that the fix in #26 still applies as expected. Would that be the preferred error flow here?

On the opposite end of spectrum, what is the maximum file size that should be supported? We could just rely on malloc erroring out in that case but that may not be sufficient. Is there a reasonable maximum threshold? Or is this out-of-scope here anyway since the user is supplying the file?

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