[Bug 214488] mqueuefs mq_setattr() leaks stack memory

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=214488

            Bug ID: 214488
           Summary: mqueuefs mq_setattr() leaks stack memory
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: vlad902+spam at gmail.com
                CC: freebsd-security at FreeBSD.org

Created attachment 176971
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=176971&action=edit
Example trigger

In kern/uipc_mqueue.c, sys_kmq_setattr() calls kern_kmq_setattr() to fill out a
struct mq_attr before copying it back to userland; however, kern_kmq_setattr()
does not zero the struct or clear the __reserved field, leaking 4 words worth
of uninitialized stack memory. The same goes for freebsd32_kmq_setattr except
it's mq_attr_to32() that does not clear __reserved in struct mq_attr32.

The mqueuefs kernel module needs to be loaded to reach this code. Example code
is attached to dump leaked memory.

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