[jira] Commented: (STDCXX-581) purify reports uninitialized memory read in __rw_memattr

["Farid Zaripov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/STDCXX-581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12536696 ] 

Farid Zaripov commented on STDCXX-581:
--------------------------------------

Commited thus: http://svn.apache.org/viewvc?rev=587117&view=rev

> purify reports uninitialized memory read in __rw_memattr
> --------------------------------------------------------
>
>                 Key: STDCXX-581
>                 URL: https://issues.apache.org/jira/browse/STDCXX-581
>             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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