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Re: Avoid use of strlen in getlogin_r (bug 22447)
- From: Carlos O'Donell <carlos at redhat dot com>
- To: Joseph Myers <joseph at codesourcery dot com>, libc-alpha at sourceware dot org
- Date: Wed, 22 Nov 2017 11:27:37 -0800
- Subject: Re: Avoid use of strlen in getlogin_r (bug 22447)
- Authentication-results: sourceware.org; auth=none
- References: <alpine.DEB.2.20.1711221730500.30870@digraph.polyomino.org.uk>
On 11/22/2017 09:31 AM, Joseph Myers wrote:
> 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.
>
> 2017-11-22 Joseph Myers <joseph@codesourcery.com>
>
> [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.
LGTM.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> diff --git a/sysdeps/unix/getlogin_r.c b/sysdeps/unix/getlogin_r.c
> index 4a6a40e..ad8e911 100644
> --- a/sysdeps/unix/getlogin_r.c
> +++ b/sysdeps/unix/getlogin_r.c
> @@ -80,7 +80,7 @@ __getlogin_r (char *name, size_t name_len)
>
> if (result == 0)
> {
> - size_t needed = strlen (ut->ut_user) + 1;
> + size_t needed = __strnlen (ut->ut_user, UT_NAMESIZE) + 1;
>
> if (needed > name_len)
> {
> @@ -89,7 +89,8 @@ __getlogin_r (char *name, size_t name_len)
> }
> else
> {
> - memcpy (name, ut->ut_user, needed);
> + memcpy (name, ut->ut_user, needed - 1);
> + name[needed - 1] = 0;
> result = 0;
> }
> }
>
--
Cheers,
Carlos.