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Date: Sat, 12 Jul 2014 15:20:17 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Cc: Brent Cook <bcook@...nbsd.org>
Subject: Re: [PATCH] implement issetugid(2)

On Sat, Jul 12, 2014 at 11:55:06AM -0600, Brent Cook wrote:
> >From OpenBSD 2.0 and later
> http://www.openbsd.org/cgi-bin/man.cgi?query=issetugid&sektion=2
> ---
>  include/unistd.h       | 1 +
>  src/unistd/issetugid.c | 9 +++++++++
>  2 files changed, 10 insertions(+)
>  create mode 100644 src/unistd/issetugid.c
> 
> diff --git a/include/unistd.h b/include/unistd.h
> index bb19cd8..30290c3 100644
> --- a/include/unistd.h
> +++ b/include/unistd.h
> @@ -109,6 +109,7 @@ uid_t geteuid(void);
>  gid_t getgid(void);
>  gid_t getegid(void);
>  int getgroups(int, gid_t []);
> +int issetugid(void);
>  int setuid(uid_t);
>  int setreuid(uid_t, uid_t);
>  int seteuid(uid_t);
> diff --git a/src/unistd/issetugid.c b/src/unistd/issetugid.c
> new file mode 100644
> index 0000000..8c81336
> --- /dev/null
> +++ b/src/unistd/issetugid.c
> @@ -0,0 +1,9 @@
> +#include <errno.h>
> +#include <unistd.h>
> +#include <sys/auxv.h>
> +
> +int issetugid(void)
> +{
> +	errno = 0;
> +	return !(getauxval(AT_SECURE) == 0 && errno != ENOENT);
> +}
> --
> 1.9.1

If this interface is to be added, it should be consistent with the
internal logic and use libc.secure, not getauxval(AT_SECURE). The
proposed code above presumably gives false positives for old kernels
where AT_SECURE did not exist, whereas the internal libc logic also
checks AT_E?[UG]ID.

Rich

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