Re: [PATCH] Remove __wur from setfsuid and setfsgid.

[Florian Weimer <fweimer at redhat dot com>]

On 04/18/2013 06:45 AM, Adam Conrad wrote:
> This is a partial revert of 7e66ee5142deda977163d0a858c3d2883cae3f07,
> which added __wur to ten set*id functions.
>
> The other eight functions have clear and sane returns that people
> should be checking, however, the setfs*id functions do not, according
> to their manpages:
>
> RETURN VALUE
>         On success, the previous value of fsgid is returned.  On error,
>         the current value of fsgid is returned.
>
> RETURN VALUE
>         On success, the previous value of fsuid is returned.  On error,
>         the current value of fsuid is returned.
>
> It was suggested in a Debian build failure bug[1] that these functions
> shouldn't have the __wur attribute, and I'm inclined to agree.

Unfortunately, the prepare_cred() call in the kernel implementation 
allocates memory and calls into the LSM framework, so these functions 
can actually fail.  But it's true that it's impossible to detect failure 
by looking at the return value.  Callers have to call getfsuid() and 
getfsgid() to check that the IDs where actually changed.

Therefore, I think the patch is correct (as correct it can be).

--
Florian Weimer / Red Hat Product Security Team