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From "Farid Zaripov (JIRA)" <>
Subject [jira] Commented: (STDCXX-581) purify reports uninitialized memory read in __rw_memattr
Date Mon, 22 Oct 2007 15:02:50 GMT


Farid Zaripov commented on STDCXX-581:

Commited thus:

> purify reports uninitialized memory read in __rw_memattr
> --------------------------------------------------------
>                 Key: STDCXX-581
>                 URL:
>             Project: C++ Standard Library
>          Issue Type: Improvement
>          Components: Test Driver
>            Reporter: Travis Vitek
>            Assignee: Travis Vitek
>             Fix For: 4.2.1
>         Attachments: 0.char.log, stdcxx-581.patch
> __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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