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Date: Wed, 10 Oct 2012 18:14:36 +0200
From: Stefan Weil <sw@weilnetz.de>
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Subject: Re: [Qemu-devel] [PATCH] virtfs-proxy-helper: check return code of
 setfsgid/setfsuid
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-trivial@nongnu.org, qemu-devel@nongnu.org

Am 10.10.2012 13:32, schrieb Paolo Bonzini:
> Fixes the following error with glibc 2.16 on Fedora 18:
>
> virtfs-proxy-helper.c: In function =E2=80=98setfsugid=E2=80=99:
> virtfs-proxy-helper.c:293:13: error: ignoring return value of =E2=80=98=
setfsgid=E2=80=99, declared with attribute warn_unused_result [-Werror=3D=
unused-result]
> virtfs-proxy-helper.c:294:13: error: ignoring return value of =E2=80=98=
setfsuid=E2=80=99, declared with attribute warn_unused_result [-Werror=3D=
unused-result]
> cc1: all warnings being treated as errors
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   fsdev/virtfs-proxy-helper.c | 8 ++++++--
>   1 file modificato, 6 inserzioni(+), 2 rimozioni(-)
>
> diff --git a/fsdev/virtfs-proxy-helper.c b/fsdev/virtfs-proxy-helper.c
> index f9a8270..b34a84a 100644
> --- a/fsdev/virtfs-proxy-helper.c
> +++ b/fsdev/virtfs-proxy-helper.c
> @@ -290,8 +290,12 @@ static int setfsugid(int uid, int gid)
>           CAP_DAC_OVERRIDE,
>       };
>  =20
> -    setfsgid(gid);
> -    setfsuid(uid);
> +    if (setfsgid(gid) !=3D 0) {
> +        return -1;
> +    }

Wouldn't setfsgid(gid) =3D=3D gid be also ok?

I have no idea whether it is a realistic scenario to call
that function with a gid which is already set.


> +    if (setfsuid(uid) !=3D 0) {
> +        return -1;
> +    }
>  =20

The same question applies here.

>       if (uid !=3D 0 || gid !=3D 0) {
>           return do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0);

The Linux manpage for both functions says something
completely different. Extract from manpage of setfsuid:

"On success, the previous value of fsuid is returned.
  On error, the current value of fsuid is returned."

In reality, the functions return 0 when called by root.

Regards

Stefan