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Date: Mon, 12 Feb 2024 12:34:06 +0200
From: "Dmitry V. Levin" <ldv@altlinux.org>
To: devel@lists.altlinux.org
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Subject: Re: [devel] I: brp-verify-unit: "... assumes overflowugid
 credentials"
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On Mon, Feb 12, 2024 at 08:58:30AM +0300, Anton Farygin wrote:
> On 12.02.2024 01:12, Dmitry V. Levin wrote:
> > Кто-нибудь может мне рассказать, почему ядро до сих пор ещё разрешает
> > setuid(overflowuid)?  Это же по сути отменяет саму идею, заложенную
> > в overflowuid.
> >
> Сейчас при входе в систему доменным пользователем UID получается 32-х 
> битный.
> 
> overflow оно только на старых системах, где UID/GID 16-бит.

Всё обстоит несколько иначе.  Не готов читать лекцию, желающие могут
обратиться к первоисточнику самостоятельно:

linux$ git grep overflowuid
Documentation/admin-guide/sysctl/fs.rst:overflowgid & overflowuid
Documentation/admin-guide/sysctl/kernel.rst:overflowgid & overflowuid
Documentation/filesystems/idmappings.rst:third idmapping. The kernel will report unmapped ids as the overflowuid
drivers/gpu/drm/drm_ioctl.c:		client->uid = overflowuid;
fs/sysctls.c:		.procname	= "overflowuid",
fs/sysctls.c:		.data		= &fs_overflowuid,
fs/udf/super.c:	uopt.uid = make_kuid(current_user_ns(), overflowuid);
include/linux/highuid.h:extern int overflowuid;
include/linux/highuid.h:#define high2lowuid(uid) ((uid) & ~0xFFFF ? (old_uid_t)overflowuid : (old_uid_t)(uid))
include/linux/highuid.h:extern int fs_overflowuid;
include/linux/highuid.h:#define fs_high2lowuid(uid) ((uid) & ~0xFFFF ? (uid16_t)fs_overflowuid : (uid16_t)(uid))
include/linux/uidgid.h:		uid = overflowuid;
include/uapi/linux/bpf.h: * 		time-wait or a request socket instead), **overflowuid** value
include/uapi/linux/bpf.h: * 		is returned (note that **overflowuid** might also be the actual
kernel/sys.c:int overflowuid = DEFAULT_OVERFLOWUID;
kernel/sys.c:EXPORT_SYMBOL(overflowuid);
kernel/sys.c:int fs_overflowuid = DEFAULT_FS_OVERFLOWUID;
kernel/sys.c:EXPORT_SYMBOL(fs_overflowuid);
kernel/sysctl.c:		.procname	= "overflowuid",
kernel/sysctl.c:		.data		= &overflowuid,
kernel/user_namespace.c: *	If @kuid has no mapping in @targ overflowuid is returned.
kernel/user_namespace.c:		uid = overflowuid;
net/core/filter.c:		return overflowuid;


-- 
ldv