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From "Travis Vitek (JIRA)" <>
Subject [jira] Created: (STDCXX-581) purify reports uninitialized memory read in __rw_memattr
Date Mon, 08 Oct 2007 21:45:50 GMT
purify reports uninitialized memory read in __rw_memattr

                 Key: STDCXX-581
             Project: C++ Standard Library
          Issue Type: Improvement
          Components: Test Driver
            Reporter: Travis Vitek
            Assignee: Travis Vitek
             Fix For: 4.2.1

__rw_memattr() checks that a specified block of memory is addressable for reading or writing.
It takes a pointer and a length. If the length is _RWSTD_SIZE_MAX, then it is assumed that
the pointer refers to a null terminated string and the number of bytes is counted via a call
to memchr() or strchr(). Unfortunately, sof the formatted io functions in printf.cpp cause
__rw_memattr() to unnecessarily touch uninitialized memory or even worse to look for the null
terminator in a buffer that is not null terminated.

An example of this is _rw_fmtlong(). It allocates a buffer of 130 chars and formats a long
value into that buffer without null terminating the buffer [it appears that this is intentional].
It then calls _rw_fmtstr() on the result. Internally _rw_fmtstr() calls __rw_memattr() with
_RWSTD_SIZE_MAX as the number of bytes to verify read/write access to. Because the buffer
is not null terminated, the __rw_memattr() call could walk past the end of the array looking
for a null terminator.

I believe that the call to __rw_memattr() in _rw_fmtlong() should be getting the actual length
of the string that is being formatted so as to avoid reading past the end of the source array.
I see no reason to allow __rw_memattr() to go looking for a null terminator when we don't
know that there is one there. This same problem occurs in _rw_fmtwstr() and _rw_fmtarray().

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