[Bug build/22447] unsafe call to strlen with a non-string in getlogin_r.c

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https://sourceware.org/bugzilla/show_bug.cgi?id=22447

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4bae615022cb5a5da79ccda83cc6c9ba9f2d479c

commit 4bae615022cb5a5da79ccda83cc6c9ba9f2d479c
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Nov 22 18:44:23 2017 +0000

    Avoid use of strlen in getlogin_r (bug 22447).

    Building glibc with current mainline GCC fails, among other reasons,
    because of an error for use of strlen on the nonstring ut_user field.
    This patch changes the problem code in getlogin_r to use __strnlen
    instead.  It also needs to set the trailing NUL byte of the result
    explicitly, because of the case where ut_user does not have such a
    trailing NUL byte (but the result should always have one).

    Tested for x86_64.  Also tested that, in conjunction with
    <https://sourceware.org/ml/libc-alpha/2017-11/msg00797.html>, it fixes
    the build for arm with mainline GCC.

        [BZ #22447]
        * sysdeps/unix/getlogin_r.c (__getlogin_r): Use __strnlen not
        strlen to compute length of ut_user and set trailing NUL byte of
        result explicitly.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                 |    7 +++++++
 sysdeps/unix/getlogin_r.c |    5 +++--
 2 files changed, 10 insertions(+), 2 deletions(-)

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