claws-mail -- no bounds checking on the output buffer in conv_jistoeuc, conv_euctojis, conv_sjistoeuc

DrWhax reports:

So in codeconv.c there is a function for Japanese character set conversion called conv_jistoeuc(). There is no bounds checking on the output buffer, which is created on the stack with alloca() Bug can be triggered by sending an email to TAILS_luser@riseup.net or whatever. Since my C is completely rusty, you might be able to make a better judgment on the severity of this issue. Marking critical for now.

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